Hippopotamus - an overview | ScienceDirect Topics (2024)

Hippopotamus

Behavioral sleep was examined in a group of three (mother, father, and their 2-month-old calf) hippopotamuses (order Artiodactyla, Hippopotamus amphibius) in a zoo. They slept both on land and in water. When in water the hippos slept while standing or lying on the bottom of pools in shallow places holding their heads above the surface and breathing regularly and only rarely lowering their heads below the surface. REM sleep occurred when the animals submerged their heads and laid on the bottom of the pool for up to 3min. The total amount of behavioral sleep in the calf was greater than in its mother, who was very protective of her baby at all times, frequently opening both eyes while asleep.

C Marine Mammals

Mammals have made the evolutionary transition from a terrestrial existence to an aquatic habitat at least three times. Cetaceans (dolphins, porpoises, and whales) are most closely related to hippopotamuses; pinnipeds (seals and the walrus) and the sea otter (Enhydra lutris) are derived members of the Carnivora; sirenians (manatees and the dugong) are the sisters of elephants (Arnason et al., 2002). These animals sleep in the sea, but how? The question is not trivial, since these mammals must maintain their nares (or blowholes) above the surface of the water to respire atmospheric oxygen, yet also have to meet their biological requirements for sleep. The bottlenose dolphin (Tursiops truncatus), Amazonian river dolphin (Inia geoffrensis), harbor porpoise (Phocoena phocoena), beluga whale (Delphinapterus leucas), and presumably all other cetaceans obtain their daily amount of sleep by engaging in SWS with one-half of their brain at a time, or unihemispherically (Lyamin, Manger, Ridgway, Mukhametov, & Siegel, 2008; see Chapter 25, this volume). During unihemispheric SWS, one hemisphere shows slow waves, and the other shows wake-related EEG activation. Bihemispheric SWS has never been observed for more than a few seconds in cetaceans, such that unihemispheric SWS is the main form of sleep in these animals. In order for each hemisphere to obtain some sleep, both hemispheres are capable of being the one engaged in SWS. This asymmetry in brain state is mirrored by an asymmetry in eye state. The eye contralateral to the sleeping hemisphere is closed, while the other eye, which sends projections to the awake hemisphere, remains open. Unihemispheric SWS allows cetaceans to swim continuously and monitor the local environment with the open eye (Gnone, Moriconi, & Gambini, 2006). For instance, captive Pacific white-sided dolphins (Lagenorhynchus obliquidens) and mother-calf pairs of bottlenose dolphin orient the open eye toward the other members of the pod, presumably to maintain group cohesion (Goley, 1999; Sekiguchi, Arai, & Kohshima, 2006).

Cetaceans might be the only mammals to have secondarily lost REM sleep (Lyamin et al., 2008). A REM sleep-like state has been reported just once, as a single bout, from a captive pilot whale (Globicephala macrorhynchus) and published as an abstract. Whether this episode truly reflected REM sleep or simply an awakening from sleep remains unknown, as all other EEG-based studies of cetacean sleep have not reported REM sleep. The continuous swimming of cetaceans might be incompatible with REM sleep, since REM sleep-related muscle atony would interfere with powered movement (but see Rattenborg et al., 2016). It is also possible that unihemispheric sleep removes the need for REM sleep. It has been proposed that a function of REM sleep is to warm the central nervous system, including the brain stem (Wehr, 1992). Animals that sleep only unihemispherically might maintain an optimal brain stem temperature from sustained (unihemispheric) wakefulness (Lyamin et al., 2018), although this idea has yet to be tested with measurements of brain stem temperature. A further possibility is that REM sleep exists only in a rudimentary form in cetaceans that has yet escaped detection. As discussed, sleeping monotremes show cortical slow waves occurring together with brain stem REM sleep-like activity (Siegel et al., 1996). For these reasons, there would be value in recording brain stem unit activity and temperature to shed light onto the presence (or extent) of REM sleep in cetaceans.

Although bihemispheric sleep is rare in cetaceans, behavioral observations from cetaceans without EEG electrodes raises the possibility that it does (or can) occur. Captive bottlenose dolphins, beluga, killer (Orcinus orca), and (juvenile) gray whales (Eschrichtius robustus) have been observed resting, either floating motionless at the water's surface or lying on the bottom of their pool. Similar reports exist for wild cetaceans, including horizontal logging in humpback whales (Megaptera novaeangliae) (Friedlaender, Tyson, Stimpert, Read, & Nowacek, 2013) and vertical logging in sperm whales (Physeter macrocephalus) (Miller, Aoki, Rendell, & Amano, 2008). Whether these animals are engaged in unihemispheric SWS, bihemispheric SWS, REM sleep or even wakefulness is unknown.

Seals can be divided into two mains group: otariid (or eared) seals and phocid (or earless) seals. These two types of seal sleep in different ways (Lyamin et al., 2008). Phocid seals retain the bihemispheric SWS (and REM sleep) of their terrestrial ancestors while sleeping on land or at sea. A study on wild Pacific northern elephant seals (Mirounga angustirostris) suggests that phocids can even sleep while diving (Mitani et al., 2010). This discovery was made by fitting elephant seals with a data logger that measured speed, depth, and three-dimensional acceleration. The animals were found to slowly drift downward following circular trajectories that resembled a falling leaf. During the descent, the seals wobbled slightly in the absence of flipper strokes. Interestingly, the animals could impact the sea bottom and remain immobile for many minutes, raising the possibility that they were asleep on the descent, unaware of the approaching sea floor.

In contrast to the obligatory bihemispheric sleep of phocid seals, otariid seals can engage in SWS both unihemispherically (like cetaceans) and bihemispherically (like phocid seals). The northern fur seal (Callorhinus ursinus) engages in bihemispheric and unihemispheric sleep on land and switches to sleeping mostly unihemispherically in the water (Lyamin et al., 2018). The use of unihemispheric SWS in seawater is apparently an adaptation to maintain their nares above the surface of the water to breathe (Lyamin et al., 2008). Specifically, the flipper sending projections to the awake hemisphere remains in the water, paddling, while the flipper contralateral to the asleep hemisphere is immobile. The amount of REM sleep drops substantially while sleeping in seawater (Lyamin et al., 2018). On land, seals engaged in 80 minutes of REM sleep per day but only 3 minutes per day in water. Some animals forgo REM sleep for days at a time. Not only was there a profound reduction in the amount of REM sleep over the 2 weeks in the water, but also the animals did not recover lost REM sleep when allowed to sleep on land. Lyamin et al. (2018) suggested that seals and other marine mammals may have no need for REM sleep when they are sleeping unihemispherically. If REM sleep functions to elevate brain stem temperature and unihemispheric wakefulness keeps the brain stem warm, then unihemispheric sleep while in the water would remove any need for REM sleep (see also Wehr, 1992). Sleep has also been studied in the walrus (Odobenus rosmarus). As a close relative of otariid seals, perhaps, it is not surprising that walruses engage in bihemispheric and unihemispheric SWS and a large reduction in the amount of REM sleep while sleeping in seawater (Lyamin et al., 2008).

The third group of marine mammals for which electrophysiologically defined sleep data exist is the sirenians, a group that includes manatees. Like otariid seals and the walrus, manatees (Trichechus spp.) have evolved the ability to engage in bihemispheric and unihemispheric SWS and small amounts of REM sleep (Lyamin et al., 2008).

Taken together, the convergent evolution of unihemispheric SWS in three groups of marine mammals—cetaceans, otariid seals and the closely related walrus, and manatees—suggests that it evolved to allow these aquatic animals to both sleep and respire at sea. Importantly, this also demonstrates that SWS must serve an inescapable function. Instead of evolving sleeplessness, these animals evolved an elegant mechanism to achieve their daily amount of SWS. Moreover, that these animals are able to continue paddling or swimming while asleep indicates that the biological target of sleep must lie within the brain. Such research further suggests that sleep is fundamentally a local process, below the level of the whole brain (Oleksenko, Mukhametov, Polyakova, Supin, & Kovalzon, 1992), a view consistent with local sleep homeostasis (Huber et al., 2004, 2006; Lesku, Vyssotski, Martinez-Gonzalez, Wilzeck, & Rattenborg, 2011) and hypotheses for the function of SWS (Tononi & Cirelli, 2014). In contrast, the loss of REM sleep in cetaceans and fur seals sleeping in seawater for weeks suggests that the function of REM sleep either is less essential than that of SWS, is no longer needed, or can be fulfilled by some other mechanism.

6 Amphibian Monogenean Cultures

Monogenean parasites of amphibians include polyopisthocotylean genera in the Polystomatidae Gamble, 1896, one of the most diverse families of the Monogenea, whose members also infest Australian lungfish, freshwater turtles and the African hippopotamus. Amphibians can live in terrestrial environments which preclude transmission of monogeneans. Thus, polystomes that infect amphibians typically store eggs in utero with egg laying and transmission in the wild restricted to the period spent by the host in water. Polystomes are oviparous, with some species exhibiting ovoviviparity: a mode of reproduction in which embryos develop inside the eggs and remain in the parent body until release, when the eggs can hatch almost immediately (Tinsley, 1983). Adult polystomes typically attach to the bladder of amphibians using paired haptoral suckers and extract blood from blood vessels in the bladder wall.

A successful amphibian polystome culture requires the supply of adult host amphibians (i.e. frogs/toads) and tadpoles. Adult amphibians and frogspawn are typically collected from the wild to establish cultures. Raising tadpoles from frogspawn also enables a source of parasite-free animals for experimental purposes. Frogspawn should be incubated at optimum temperatures in aerated water and resulting tadpoles reared in the same conditions with water renewed periodically (Badets et al., 2009, 2013). To identify adult amphibians infected with bladder parasites, they can be isolated in tanks or containers containing small amounts of water that is observed daily under a dissection microscope for eggs released with the urine flow (Badets et al., 2013; Theunissen et al., 2014; Fig. 1). Eggs are incubated in clean, dechlorinated freshwater and, when fully formed, oncomiracidia can be seen moving within eggs. Theunissen et al. (2014) found that Protopolystoma xenopodis Price, 1943 eggs rapidly hatch following brief exposure to direct sunlight. Active swimming oncomiracidia can be cohabited with susceptible tadpoles and, with some exceptions (see below), will remain attached to the gills until host metamorphosis. Kok and Du Preez (1987) found they could examine the location and numbers of parasites present in sedated Natalobatrachus bonebergi Hewitt and Methuen, 1913 tadpoles through in vivo microscopic examination of the gills. A minimal amount of pigment laid down in the ventral body wall of N. bonebergi enabled examination at any time without killing the hosts and the destiny of individual parasites could be followed up to metamorphosis (Kok and Du Preez, 1987).

Egg production in Polystoma Zeder, 1800 and Metapolystoma Yamaguti, 1963 coincides with the brief spawning period spent in water by otherwise terrestrial anuran hosts. Polystoma nearcticum (Paul, 1935) exhibits remarkable reproductive synchrony with its tree frog host, Hyla versicolor LeConte, 1825, and becomes reproductively active only during the short period of host sexual activity at spawning (Armstrong et al., 1997). Reproduction is typically short lived in Polystoma and Metapolystoma with ~90% of the total annual egg production taking place in 4 days (Tinsley, 1983) and some of the fastest egg production observed in monogeneans (e.g. Polystoma integerrimum (Frölich, 1791) may produce up to 2500 eggs in 24h or ~2 eggs/min; Combes, 1972).

Parasites in Polystoma and Metapolystoma exhibit two alternative phenotypes depending on the age of infection of amphibians, providing an intriguing model for examining life cycle evolution in monogeneans. The ‘branchial’ phenotype includes parasites that attach to young tadpoles and exhibit accelerated development while still in the branchial chamber, prior to death at the time of metamorphosis of the tadpoles. The ‘bladder’ phenotype includes oncomiracidia that migrate to the urinary bladder, where they reach sexual maturity 3 years later, and release eggs that are flushed out with the host urine. These two phenotypes can be produced in vivo as long as there is an adequate source of recently hatched tadpoles. Badets et al. (2009) showed that the branchial phenotype is typically achieved by exposing <7-day-old Hyla meridionalis Boettger, 1874 tadpoles to Polystoma gallieni Price, 1938 oncomiracidia and the bladder phenotype is exhibited in tadpoles infected at >14 days old.

2 A Brief Background on Fascioliasis and the Biology of Fasciola Species

Liver flukes are important parasitic flatworms (Platyhelminthes: Trematoda) affecting animals in a wide range of countries. Fasciola spp. are known to infect a wide variety of mammals (definitive hosts), including ruminants, suidians, primates, elephants, hippopotami, lagomorphs and rodents (Mas-Coma et al., 2009; Menard et al., 2000), some being more permissive than others. The two representatives of most key socioeconomic importance are F. hepatica and Fasciola gigantica. These two species are usually the causative agents of fascioliasis in livestock, wildlife and humans (Mas-Coma et al., 2009; Torgerson and Claxton, 1999). Fascioliasis is recognized as a neglected disease and occurs mainly in parts of Africa, the Middle East, South America and Southeast Asia (Mas-Coma, 2005; Mas-Coma et al., 2009).

F. hepatica and F. gigantica are similar morphologically and biologically (Itagaki et al., 2009; Le et al., 2008; Peng et al., 2009). Both Fasciola spp. have di-heteroxenous life cycles, which involve (freshwater) lymnaeid snails as intermediate hosts and mammals as definitive hosts (Andrews, 1999). Differences in host specificity between F. gigantica and F. hepatica appear to define the aetiology and clinical manifestation of disease in the definitive host (Spithill et al., 1999). A key difference between these parasites is their adaptation to different intermediate snail hosts, linked to the geographic distribution of these parasites and disease. F. hepatica often utilizes snails such as Lymnaea tomentosa and Galba truncatula, which are widespread in temperate and subtropical climes (Mas-Coma et al., 2009). F. gigantica usually prefers snails, including Radix rubiginosa and R. natalensis, which live in the subtropics and tropics. In subtropical regions, both species of Fasciola can coexist, and fascioliasis can also be associated with Fasciola sp. (a proposed F. gigantica×F. hepatica hybrid) (cf. Mas-Coma et al., 2009; Spithill et al., 1999).

Malaysia

The vertebrate fossils in Peninsular Malaysia are rather poorly known. The first known fossils originate from Tambun cave, a tin-bearing deposit near Ipoh, Kinta Valley, Perak. The fauna is composed of isolated teeth and postcranial elements of Rhinoceros sondaicus, Sus sp., Hippopotamus sp., Cervus sp., Duboisia santeng, Bubalus sp., and a small carnivore. This site was considered a middle Pleistocene age because of the presence of Duboisia, an extinct antelope, also present in Javan middle Pleistocene deposits. Recently, Batu caves in Selangor and Layang Cave complex in Pahang have delivered some late Pleistocene mammals. They consisted mainly of isolated teeth of medium- and large-sized mammals such as Pongo, Sumatran rhinoceros (Dicerorhinus sumatrensis), Malayan tapir (Tapirus indicus), pigs (Sus scrofa and Sus barbatus), Capricornis sumatraensis, Muntiacus muntjak, sun bear (Helarctos malayanus), Ursus thibetanus, Panthera tigris and Malayan civet (Viverra tangalunga). Small mammals such as murid rodents (Maxomys surifer and Chiropodomys gliroides), porcupines (Hystrix brachyura and Atherurus macrourus), bats and insectivores are also preserved (Ibrahim et al., 2013; Muhammad et al., 2019). The OSL and TL dating of deposits from Batu cave give an age range of 66–33ka (Ibrahim et al., 2013).

2.14.8 Cognition, Memory, and Intelligence

Intelligence has been defined as behavioral and cognitive flexibility as expressed in problem-solving abilities. Specific capacities for various types of memory, tool use, mirror self-recognition, gregariousness, and communication have been used as proxy measures for intelligence among species (Roth and Dicke, 2005, 2012). However, comparative cognitive data are limited, and there is not a consensus on how to interpret similarities and differences among species. Both absolute and relative brain size have been invoked as correlates of intelligence among mammals. More recent studies report that the number of cortical neurons, neuron packing density, distance between neurons, and axon conduction velocity are better indicators of intelligence (reviewed in Dicke and Roth, 2016; Herculano-Houzel, 2011; Herculano-Houzel and Kaas, 2011; Roth, 2015). Using these criteria, human and nonhuman primates have the highest “intelligence” scores. Elephants and cetaceans possess a thinner cortex with fewer cortical neurons, resulting in lower scores (Dicke and Roth, 2016; Herculano-Houzel etal., 2014). However, a recent study found that the long-finned pilot whale possesses twice the number of neocortical neurons than humans (Mortensen etal., 2014), with cautionary evidence indicating that no one neuroanatomical variable is likely to stand alone as a measure of intelligence.

Recent comparative neuroanatomical studies of large mammals including giraffes, elephants, hippopotamuses, and cetaceans (Butti etal., 2014, 2015; Jacobs etal., 2014, 2015, 2016) provide a new perspective to interpret behavioral data on these species.

Elephants are highly social with remarkable long-term memories, advanced problem-solving skills, and apparent rituals for their dead (Hart etal., 2008; Lee and Moss, 2012; Plotnik etal., 2006, 2010; Poole etal., 2005; Stoeger and Manger, 2014). Elephants are also one of the few mammals that have demonstrated mirror self-recognition (Plotnik etal., 2006, 2010), which is related to capacities for empathy and theory of mind in humans and great apes (Gallup, 1982, 1985; Lewis etal., 1989; Povinelli and DeBlois, 1992; Povinelli etal., 1990). In elephants, the large parietal and temporal lobes have been associated with their capacity for memory, sensory processing, and mental mapping abilities (Hart etal., 2008). Tool use has also been documented for elephants. For example, elephants have been observed using branches to wave off flies, using twigs to scratch their backs, and plugging their bells with mud to avoid making detectable noise (Hart etal., 2008).

Giraffes also exhibit complex social and behavioral characteristics. Like elephants, giraffes live in matrilineal societies with social affiliation and attachment as well as a fission–fusion social strategy (Bercovitch and Berry, 2010, 2013). A characteristic of fission–fusion social systems is complex communication. Elephants use a low-frequency communication system called infrasound that is below the human range of hearing (Garstang, 2004; Heffner and Heffner, 1982). Giraffes may also use infrasound such as the okapi, rhinoceros, elephant, and cetaceans (Baotic etal., 2015). Vocal communication in giraffes is not well understood; giraffes may produce infrasonic vocalizations similar to elephants, but acoustic studies are few, and the results have been inconclusive (Baotic etal., 2015).

Dolphins, among odontocetes, use high-frequency click trains, whistles and burst-pulses for a variety of purposes, such as echolocation, communication, navigation, and foraging. There is evidence of communication with repertoires of “signature whistles” (Janik etal., 1994; Mccowan and Reiss, 1995; Sayigh etal., 1990, 1995; Thomsen etal., 2001, 2002; Tyack, 1986), different “dialects” characterizing the vocal repertoire of different groups of dolphins, and the use of specific whistles in association with a specific social behavior (Connor and Smolker, 1996; McCowan and Reiss, 1995, 2001; Rendell and Whitehead, 2001; Sayigh etal., 1990, 1995). Odontocetes use echolocation, and mysticetes (as well as some avian species) use social transmission of songs (Payne and McVay, 1971; Webb and Zhang, 2005) that are documented to show variability over time within the same group of whales and display differences in themes and phrases between geographically isolated populations (Helweg etal., 1998). There is also a cultural passage of songs among whale populations, as is seen in humpback whales, where songs are passed from populations in the west to populations in the east (Garland etal., 2011). Cetaceans, like elephants, exhibit complex social behaviors, mirror self-recognition, cooperation, and tool use (Delfour and Marten, 2001; Marino, 2002, 2004; Payne and McVay, 1971; Reiss and Marino, 2001; Rendell and Whitehead, 2001); they have the capacity to imitate sounds and behaviors (Hooper etal., 2006; Reiss and Mccowan, 1993; Richards etal., 1984; Tayler and Saayman, 1973), understand artificial language as sequences of acoustic or gestural codes, and demonstrate understanding of pointing gestures and syntactic features (Harley etal., 1996; Herman etal., 1999, 1993, 1990, 1998, 1984; Pack and Herman, 1995, 2007; Pack etal., 2002; Tschudin etal., 2001). Dolphins display strong short-term auditory, visual, and spatial memory as well as long-term memory involving the structure of relationship between individuals in the same group (Connor, 2007; Herman, 1975; Reiss and McCowan, 1993; Richards etal., 1984; Thompson and Herman, 1977), and they are known to show, like elephants, behaviors consistent with empathy (Balfour and Balfour, 1997; Connor and Norris, 1982; Poole and Moss, 2008).

Very little is known about the behavior of hippopotamuses, but there is evidence for elaborate vocal repertoire made of sounds that can be transmitted and received in the air and in water simultaneously (the so-called “amphibious communication”) and that include clicks and pulses comparable to those of cetaceans (Barklow, 1997, 2004). However, these behavioral observations were made on the large and gregarious river hippopotamus, and there is no evidence that such observations could be extended to the smaller, solitary, and more elusive pygmy hippopotamus.

The body of behavioral evidence for cognitive abilities in cetaceans, elephants, giraffes, and hippopotamuses suggests that advanced cognitive processes evolved in these groups of mammals independently and that evolution can shape different cortical organizations to lead to similar functional outcomes across these species to generate cognitive abilities that are comparable overall.

Cleaning Symbiosis

Hosts use a variety of behavioral methods to rid themselves of parasites. Preening of birds, bathing of birds in dust and water, and passive and active anting (letting ants passively crawl over the body or actively squeezing ants over the plumage, respectively) are thought to help in reducing parasite loads, although evidence is scarce. Some other behavioral patterns (dolphins rubbing against rocks, fish jumping out of the water, etc.) may also play a role. Most widely distributed and well studied, particularly in the marine environment, is cleaning symbiosis, in which one animal (the cleaner) cleans another (the host), removing its parasites and diseased tissues. Birds remove ticks and other ectoparasites from cattle, hippopotamus, and even large marine fish floating on the surface, and several species of shrimps, as well as greater than 100 species of fish, are cleaners in freshwater but mainly in the sea. Besides fishes, the Galapagos marine iguana, whales and dolphins, invertebrates, etc. are hosts to cleaners. Cleaner fish often have special morphological adaptations, such as a terminal mouth and fused anterior teeth and conspicuous color patterns, the so-called guild signs. In addition, the Indo-Pacific cleaner wrasse, L. dimidiatus, performs a cleaning dance that attracts host fish. Hosts, on their part, show invitation postures signaling to the cleaner that they are ready to be cleaned, and fish of many species, usually hostile to each other, queue peacefully up at cleaning stations (territories where cleaning occurs). They even allow cleaners to enter their mouth cavity. In well-established cleaning symbioses, hosts rarely or never eat cleaners. Some fish were observed to spend as much time at cleaning stations as they spend on feeding, and some cleaner species feed exclusively on parasites and diseased host tissue. Certain fish mimic the color pattern and behavior of cleaners to approach hosts in order to attack them and bite off pieces of the fin or skin.

Post-Compacting Morula and ICM Specification From Inner Cells

At the 16-cell stage, the mouse embryo contains on average three inside cells (Samarage etal., 2015), which are smaller and have larger nucleo-cytoplasmic ratios than the outside cells (Aiken etal., 2004). This spatial segregation creates two discrete niches, exposing inner and outer cells to different microenvironments and cell–cell contacts. Once these subpopulations of inside vs outside cells have been firmly established in the morula, their different cell positions instruct differences in cell signaling, transcriptional activity and ICM vs TE specification.

Activation of Hippo signaling depends on basolateral cell–cell junctions and the absence of an apical membrane domain, which are conditions only found in internalized cells. How does lack of an apical domain activate Hippo signaling in inner cells while presence of an apical domain suppresses it in outer cells? The answer lies in sequestration of key members of the pathway by proteins that regulate adhesion and polarity. AMOT and NF2 are required to activate Hippo kinases LATS1/2 and switch on Hippo signaling. AMOT and LATS1/2 kinases are both inactive as long as they are apically localized, preventing activation of the Hippo pathway in outer cells. In inner cells, which lack an apical domain, AMOT localizes to adherens junctions, interacting with E-cadherin via NF2 and binding LATS1/2. LATS1/2 then phosphorylates and activates AMOT at the adherens junctions, in turn phosphorylating YAP/TAZ. Phosphorylated YAP/TAZ is excluded from the nucleus and degraded. Consequently, YAP/TAZ cannot co-activate TEAD4, resulting in failure to induce the TE program via Cdx2 expression. In this way, inner cells switch on Hippo signals to inactivate YAP/TAZ and allow expression of ICM genes. Without any NF2, the Hippo pathway cannot be activated and such embryos fail to form an ICM. Regardless of their position, inner cells then revert to expressing TE genes instead. In summary, cell position and polarity are mutually reinforcing properties. Hippo signals consolidate differences in cell polarity and position through transcription factor activation, driving the first lineage bifurcation by converting inside cells into ICM and outside cells into TE.

The relationship between cell polarity and cell fate has been further probed by sequentially separating blastomeres after each cell division from the 2-cell to the 32-cell stage, thereby completely inhibiting cell–cell contact and positioning (Lorthongpanich etal., 2012). Each singled out cell adopts a unique gene expression pattern, representing a random mixture of ICM- and TE-specific genes, but overall leaning towards a TE-like profile. Isolated cells also preferentially contribute to TE in morula aggregation experiments. This is consistent with early observations that isolated 8-cell blastomeres give rise to functional TE but do not form ICM-derivatives. On their own, these blastomeres depolarize and consequently activate Hippo/YAP signaling. However, such blastomeres still become biased towards TE, despite the loss of apicobasal polarity and active Hippo signals. Thus lack of an apical domain and Hippo signals are insufficient to entirely control the first lineage decision and induce ICM commitment. Collectively, these data suggest that cell–cell interactions and positional information provide additional cues that are important for correct cell fate specification.

After the 16-cell stage, inner cells expand in numbers while retaining their internal position. At the same time, new inner cells continue to be added by apical constriction and asymmetric divisions of outer cells (Samarage etal., 2015).

Madagascar

Madagascar has been isolated from Africa for at least 140 million years, and from India for around 88 million years. It has a rich flora in which about 84% of the species are endemic, and in at least some cases their closest relatives occur in southern Asia rather than Africa. There are five endemic plant familes and 321 endemic genera. The isolation of Madagascar predated the major adaptive radiation of mammals that has occurred in Africa, and it lacks large grazing mammals – although a dwarf hippopotamus appears to have become extinct less than 1000 years ago – and large carnivores.

At present the largest wild mammal is the bush pig (Potamocho*rus larvatus), which is believed to be a recent arrival. A group of primitive primates, the lemurs, has radiated into all the habitats on the island. Fossils show that they were formerly even more diverse than they are now; some extinct forms were much larger than any modern species. The largest carnivore is the fossa (Cryptoprocta ferox), a large mongoose-like animal that climbs trees well and is a specialist predator on lemurs. There are also fossil and subfossil remains of giant flightless birds (Aepyornis), the last of which seem to have become extinct only a few hundred years ago. Humans reached the island from the east perhaps 1500 years ago. At first their settlements were confined to the coast, but later they spread inland and colonized the central plateau. Humans have had a dramatic effect on the island's natural vegetation and habitats.

Flowering plants were in their earliest stages of evolution when the island became isolated, and a high percentage of species (80% in the legumes, Fabaceae), many genera, and some families are endemic. The vegetation of the island is very varied. On the eastern side, rainfall is high and there is little or no dry season. Here there are tropical rain forests, very diverse in composition, with no single species being dominant. They differ from the forests of mainland Africa in their lower stature (25–30m), lack of large emergent trees, the abundance of small palms in the understory, and the frequent occurrence of climbing bamboos. These forests have been considerably reduced by clearance for agriculture, and only scattered fragments remain. Secondary forests are widespread, often characterized by the distinctive traveler's tree (Ravenala madagascariensis), with a single stem crowned by huge leaves arranged like a fan in two opposite rows. Higher up the forest takes on a more montane aspect; the trees are shorter and more branched, and epiphytic ferns and mosses are abundant. The highest mountains support a montane thicket of small-leaved ericoid shrubs such as Erica (Ericaceae), Stoebe (Asteraceae), and everlastings (Helichrysum, Asteraceae) (Koechlin et al., 1974).

A drier form of forest or woodland seems also to have occupied much of the central plateau, but only tiny fragments remain, and these are under intense pressure from fire, agriculture, and wood cutting for charcoal. The commonest tree is tapia (Uapaca bojeri), which may owe its survival to its fire resistance. One legume genus with two species, Peltiera, has recently been described from forest fragments in this zone; only three specimens and no living plants are known and it seems likely that the genus was extinct before it was described. The forests of the central plateau have largely been replaced by a species-poor grassland that provides little protection to the soil from erosion so that gullies are widespread and deep.

In the western half of the island, dry deciduous or semideciduous forest survives here and there, particularly in limestone areas, which have often weathered to produce an inhospitable landscape of sharp ridges and pinnacles (“tsingy”) that is very difficult to access and unsuited to any kind of agriculture.

The southern end of the island, particularly in the west, is very dry, and here a peculiar thorn forest is found in which the endemic cactus-like family Didieriaceae is common. Specialized lemurs (sifakas - Propithecus verreauxi) live in this thorn forest. This remarkable vegetation type is threatened by agriculture, particularly sisal cultivation, by grazing, and by cutting for charcoal production. Perhaps because of the absence of large grazing animals, members of several plant families have developed a growth form in which leaves are absent and photosynthesis is carried out in the flattened stems. Several members of the family Fabaceae show this feature.

Another plant growth form perhaps more widely developed in the dry parts of Madagascar than in any other region is the “bottle-tree,” in which a thick and swollen trunk supports a rather small crown. The genus Adansonia, with one species in Africa (the baobab) and one or two in Australia, has seven species in Madagascar. The flame-tree (Delonix regia), now an extremely widespread ornamental tree in the tropics, is one of ten Delonix species in Madagascar, with just one other in tropical Africa. Several of the Madagascar species are bottle-trees.

Some of the richest habitats in Madagascar are the rocky outcrops, perhaps because they are sheltered from fires and grazing animals. Numerous endemic species of Aloe and succulent spurges (Euphorbia), as well as strange single-stemmed spiny succulents (Pachypodium), are common on these rocky outcrops and make them striking refuges for the remarkable flora of this isolated island.

Biomaterials

The preservation and restoration of objects made from biomaterials is particularly challenging as their degradation products are complex and diverse. Examples of problems facing museum conservators include art objects made from ivory, horn, natural resins, and textiles; these objects have often become fragile and restoration is of the utmost significance and importance. Often, earlier restorative procedures, which may have been incompletely documented, are no longer satisfactory and the results of chemical deterioration of applied restoratives under the influence of solar radiation and humidity changes in storage are sadly too often plain to see.

Similarly, IR and Raman spectroscopic studies of ancient textiles are being undertaken to derive information about the possible processes of their degradation under various burial environments, for example, Egyptian mummy wrappings, silk battle banners, Roman woollen clothing, and artistic linens from funerary depositions. A classic, topical, and ongoing controversy covers the spectroscopic studies associated with the Shroud of Turin and the nature of the pigmented areas on the ancient linen.

Ancient technologies and cultures often used naturally occurring biomaterials as decorative pigments and as functional repairing agents on pottery and glass. Recent studies have centered on the provision of a Raman spectroscopic database for native waxes and resins, which has been used for the nondestructive evaluation of archaeological items, for example, ‘Dragon’s blood’, and it is possible to identify different sources of this material from the spectra. FT-IR spectroscopy, too, has been successful in the characterization of conifer resins used in ancient amphorae and has been particularly useful for attribution of the Baltic geographical origins of amber jewelry through its succinic acid content and for the detection of modern fakes made from phenol–formaldehyde resins that are often passed off as examples of ancient ethnic jewelry.

The identification of dammar and mastic resins that have been used as spirit-soluble varnishes on paintings and on early photographic prints, and the conservation of the latter, in particular, is very important because of the embrittlement of the substrate due to exposure to light and humidity changes. Raman spectroscopy has been used to identify wax coatings on early photographs from the American Civil War (c.1865) that are showing evidence of deterioration in museum collections.