Daubentonia Research Articles

A hybrid genome assembly of the endangered aye-aye (Daubentonia madagascariensis).

The aye-aye (Daubentonia madagascariensis) is the only extant member of the Daubentoniidae primate family. Although several reference genomes exist for this endangered strepsirrhine primate, the predominant usage of short-read sequencing has resulted in limited assembly contiguity and completeness, and no protein-coding gene annotations have yet been released. Here, we present a novel, fully annotated, chromosome-level hybrid de novo assembly for the species based on a combination of Oxford Nanopore Technologies long reads and Illumina short reads and scaffolded using genome-wide chromatin interaction data-a community resource that will improve future conservation efforts as well as primate comparative analyses.

Specifically unspecific – Simple devices as feasible and effective enrichment for small mammals

Although enrichment is an essential part of modern zoo animal husbandry, research on effective enrichment for small mammals is scarce, albeit they are regularly kept in zoos. To develop solutions that are inexpensive, readily applicable, and adaptable for a variety of species, we investigate whether three types of simple enrichment devices (SEDs) – object, olfactory, and food-motivated – elicit positive interactions in various zoo-housed small mammal species. In this preliminary exploration study, we evaluate if amount of enrichment interactions, display of behavioral stress reactions, and display of stereotypic behaviors vary, if different types of SEDs are provided. Therefore, we observed 39 individuals of ten species, most of which are underrepresented in enrichment literature: Eastern quoll (Dasyurus viverrinus), round-eared elephant shrew (Macroscelides proboscideus), aardvark (Orycteropus afer), southern tamandua (Tamandua tetradactyla), northern Luzon giant cloud rat (Phloeomys pallidus), green acouchi (Myoprocta pratti), South African springhare (Pedetes capensis), aye-aye (Daubentonia madagascariensis), golden lion tamarin (Leontopithecus rosalia), and Javan mouse-deer (Tragulus javanicus) housed in Frankfurt Zoo, Germany. All focal individuals interacted with at least two types of SEDs and around 80% interacted with all types of SEDs, resulting in a considerable amount of time spent with the enrichment. There was a preference for food-motivated enrichment. Neither behavioral stress reactions nor stereotypic behaviors differed if different types of SEDs were present. Model selection showed that GLMs explaining enrichment interactions improved if the variable ‘individual’ instead of ‘species’ was included, suggesting that reactions towards unspecific SEDs might be more individual-driven than species-specific. Because individuals of all species chose to interact with the SEDs and we did not find behavioral indicators for stress elicited by the SEDs, we advocate for the regular provision of SEDs for small mammals in human care.

Aye-aye middle finger kinematic modeling and motion tracking during tap-scanning

The aye-aye (Daubentonia madagascariensis) is a nocturnal lemur native to the island of Madagascar with a unique thin middle finger. Its slender third digit has a remarkably specific adaptation, allowing them to perform tap-scanning to locate small cavities beneath tree bark and extract wood-boring larvae from it. As an exceptional active acoustic actuator, this finger makes an aye-aye’s biological system an attractive model for pioneering Nondestructive Evaluation (NDE) methods and robotic systems. Despite the important aspects of the topic in the aye-aye’s unique foraging and its potential contribution to the engineering sensory, little is known about the mechanism and dynamics of this unique finger. This paper used a motion-tracking approach for the aye-aye’s middle finger using simultaneous video graphic capture. To mimic the motion, a two-link robot arm model is designed to reproduce the trajectory. Kinematics formulations were proposed to derive the motion of the middle finger using the Lagrangian method. In addition, a hardware model was developed to simulate the aye-aye’s finger motion. To validate the model, different motion states such as trajectory paths and joint angles, were compared. The simulation results indicate the kinematics of the model were consistent with the actual finger movement. This model is used to understand the aye-aye’s unique tap-scanning process for pioneering new tap-testing NDE strategies for various inspection applications.

Biomimetic investigation of the impact of the ear canal on the acoustic field sensitivity of aye-ayes

The aye-ayes (Daubentonia madagascariensis) are an extremely rare lemur species and the world’s largest nocturnal primate. Tapping on tree bark with its unique elongated middle finger, the aye-aye listens closely for signs of cavities or insect larvae inside; this is a unique acoustic-based foraging behavior called “percussive foraging” or “tap-scanning.” Tap-scanning requires the animal auditory system to exhibit exceptional acoustic receptive field sensitivity. This study provides an insight into how the ear canal of aye-ayes might have an impact on their acoustic field sensitivity; this was achieved using a biomimetic approach to simulate the tapping mechanism. To this end, the aye-aye’s pinna and ear canal were 3D printed. The pinna in the cupped position was preserved, and the acoustic field was evaluated in the time and frequency domains. The results suggest that the pinna with the ear canal can substantially enhance the receptive field sensitivity of the aye-aye’s auditory system by shaping a focal area at the tapping location. Furthermore, changes in the sound field receiving beam pattern for higher frequencies resulted in an increase in the receiver dominant frequency, indicating the evolution of the aye-ayes’ external ear to create a physical filter for excluding unnecessary low frequencies in the focal area.

A review of nose picking in primates with new evidence of its occurrence in Daubentonia madagascariensis

AbstractNose picking (rhinotillexis) is a common behaviour in humans which remains, however, poorly studied. Several species of primates are known to pick their nose and ingest the nasal mucus suggesting that this behaviour may actually be beneficial and showing it is not restricted to humans. Here, we review relevant literature and online sources, and document the species of primates observed to pick their nose. We also present the first occurrence of this behaviour in a species of strepsirrhine primate (lemurs and relatives) with a unique video showing an aye‐aye picking its nose. While doing so this animal inserts the entire length of its extra‐long, skinny and highly mobile middle finger into the nasal passages and then licks the nasal mucus collected. We further investigate the internal anatomy of the nasal cavity of the aye‐aye in order to understand how it can introduce its entire finger in its nasal cavity and discover that the finger likely descends into the pharynx. We show that this behaviour is present in at least 12 species of primates, most of them also showing great manipulative/tool use skills and may have some associated benefits that need to be further investigated. Further comparative studies examining nose picking and mucophagy in other primate species and vertebrates in general may shed additional light on its evolution and possible functional role.

Mild movement sequence repetition in five primate species and evidence for a taxonomic divide in cognitive mechanisms

When animals forage, they face complex multi-destination routing problems. Traplining behaviour—the repeated use of the same route—can be used to study how spatial memory might evolve to cope with complex routing problems in ecologically distinct taxa. We analyzed experimental data from multi-destination foraging arrays for five species, two cercopithecine monkeys (vervets, Chlorocebus pygerythrus, and Japanese macaques, Macaca fuscata) and three strepsirrhines (fat-tailed dwarf lemurs, Cheirogaleus medius, grey mouse lemurs, Microcebus murinus, and aye-ayes, Daubentonia madagascariensis). These species all developed relatively efficient route formations within the arrays but appeared to rely on variable cognitive mechanisms. We found a strong reliance on heuristics in cercopithecoid species, with initial routes that began near optimal and did not improve with experience. In strepsirrhines, we found greater support for reinforcement learning of location-based decisions, such that routes improved with experience. Further, we found evidence of repeated sequences of site visitation in all species, supporting previous suggestions that primates form traplines. However, the recursive use of routes was weak, differing from the strategies seen in well-known traplining animals. Differences between strepsirrhine and cercopithecine strategies may be the result of either ecological or phylogenetic trends, and we discuss future possibilities for disentangling the two.

Seasonal differences in hair growth rates of captive aye-aye, red ruffed, and black-and-white ruffed lemurs.

Hair can be an important source of biological information, providing a record of such things as pollutant exposure, hormonal levels, and stable isotope ratios. Hair as a biological sample is easily accessible, easily stored, and resists degradation. Analysis of hair is particularly useful when studying rare and endangered species, such as lemurs, since it can be sampled noninvasively. However, to better interpret the results of stable isotope or other analyses, it is important to understand hair growth rates. We measured hair growth rates in captive aye-ayes (Daubentonia madagascariensis), red ruffed lemurs (Varecia rubra), and black-and-white ruffed lemurs (Varecia variegata), both in winter (December23, 2013, toJanuary13, 2014) and summer (July 10-31, 2013) at the Duke Lemur Center.Hair growth per week in all three species of lemursdiffered significantly between the boreal summer and boreal winter. The aye-aye, black-and-white ruffed lemur, red ruffed lemur had a mean weekly hair growth of 0.195, 0.209, and 0.232 cm, respectively, in the summer. While the aye-aye, black-and-white ruffed lemur, and red ruffed lemur had a mean weekly hair growth of 0.239, 0.464, and 0.479 cm, respectively, in winter. We found no effect of age on hair growth rates, neither in the boreal summer, nor in the boreal winter for black-and-white ruffed lemurs and red ruffed lemurs. A pregnant black-and-white ruffed female displayed negligible hair growth during the northern winter, suggesting that pregnancy may affect the partitioning of resources away from such things as hair growth.

Initial Reintroduction of the Aye-Aye (Daubentonia madagascariensis) in Anjajavy Reserve, Northwestern Madagascar

Madagascar’s biodiversity is imperiled by habitat loss and degradation. Furthermore, species may be locally extirpated due to targeted hunting or disease. Translocating at-risk individuals to areas devoid of the species may be an effective conservation intervention. The aye-aye, Daubentonia madagascariensis, is uniquely susceptible to hunting pressure due to a cultural superstition. In June 2018, we reintroduced two aye-ayes in the Anjajavy Reserve, a dry deciduous forest in northwestern Madagascar. The translocated individuals, an adult female and juvenile offspring, were rescued from a neighboring forest that was subjected to pressure from fires and logging. We safely secured and transported the aye-ayes to Anjajavy and put them in a quarantine enclosure, where they were subjected to biomedical and behavioral monitoring. After release in the adjacent, protected forest, we conducted postrelease monitoring of the adult female using radio-tracking and scan sampling to determine ranging and activity patterns. We conducted behavioral observations from October 2018 to February 2019 and collected sleeping site data from October 2018 to September 2019. The female aye-aye fed on local resources including Canariumsp. seeds. During the study period, the aye-aye used 31 nests, occupied a home range of approximately 85 ha and traveled, on average, at a pace of 320 m/h. Our findings are comparable with published data on wild aye-ayes in other regions of Madagascar and provide support for future reintroductions of adult aye-ayes, and potentially other endemic species to the natural and protected habitats of Anjajavy.

Locomotion of an adult female and juvenile male aye-aye (Daubentonia madagascariensis) in Torotorofotsy, Madagascar.

Aye-ayes (Daubentonia madagascariensis) locate and acquire invertebrates from within woody substrates at all levels of the rainforest; yet how their locomotion helps them accommodate this diet has not been explored in detail. We studied the locomotor behavior of an adult female (N = 1,085) and juvenile male (N = 708) aye-aye in the undisturbed forest of Torotorofotsy, Madagascar from May to December 2017. We used bout sampling to record locomotion during foraging and travel of the two radio-collared individuals. We used χ 2 tests to compare overall locomotion, travel, and foraging, as well as strata and support use. We performed a correspondence analysis to examine relationships between individual behaviors, strata, and support types. Leaping accounted for 47.9% and 50.1% of all locomotor activity in the adult female and juvenile male, respectively. Leaping was the most common behavior during travel in both individuals (59.2% and 53.9%, respectively), whereas head-first descent was most frequent during foraging (35.0% and 48.0%, respectively). For all three locomotor categories, the main canopy (40.3%-79.6%) was used most frequently and trunks were the most frequently used support type (50.7%-60.0%). There is a strong association between strata and support use overall and during travel. Quadrupedal walking was significantly associated with the main canopy, as was head-first descent with the low canopy. Our analysis demonstrates that aye-ayes use a variety of locomotor behaviors to forage for invertebrates. Aye-ayes' ability to repurpose their positional repertoire to acquire other resources in degraded forests should not obscure the importance of invertebrates to this species.

New dentaries of Chiromyoides (Primatomorpha, Plesiadapidae) and a reassessment of the “mammalian woodpecker” ecological niche

Based on their relatively large, chisel-like incisors and robust dentaries, species of the Paleocene plesiadapid mammal Chiromyoides have been described as potential ecological analogues of either seed-eating rodents or the unusually specialized lemur Daubentonia madagascariensis. Here, we analyze the most complete dentaries of Chiromyoides currently known in order to illuminate jaw form and function in this taxon. Principal Component Analysis shows that Chiromyoides campanicus and Daubentonia are uniquely similar in select dentary proportions when compared with a sample including seven other fossil plesiadapid taxa as well as 22 extant primates, dermopterans and scandentians. Comparative allometric analyses indicate that in both Daubentonia and Chiromyoides, the unique jaw proportions are likely achieved through hypertrophy of masseteric fossa length and dentary depth, rather than simple reduction of tooth row length. Consistent with these dentary features indicative of powerful gnawing, we show that incisor apex morphology became increasingly chisel-like in certain younger species of Chiromyoides. Importantly, slight reduction in molar area relative to jaw length and body mass appears to characterize all species of Chiromyoides in which molar proportions can be estimated. Notably, this pattern occurs in one of the oldest known specimens of Chiromyoides, an edentulous but relatively complete dentary from the middle Tiffanian of Texas, which differs from other Chiromyoides specimens in having a relatively shallower corpus. Taken together, this evidence suggests that Chiromyoides was a Daubentonia-like extractive forager that evolved from taxa whose diets emphasized exudates.

Developmental Timeline of Wild Aye-Aye (Daubentonia madagascariensis) Infants in Kianjavato and Torotorofotsy, Madagascar

Wild aye-ayes ( Daubentonia madagascariensis ) are notoriously difficult to study due to their solitary and nocturnal nature. While research is starting to elucidate the behaviors of wild adult aye-aye, an understanding of behaviors in young aye-ayes is still lacking. We studied the behavioral development of two male aye-aye subadults in Kianjavato, Madagascar from June 2015 to October 2017 and October 2017 to December 2019, and two male offspring in Torotorofotsy, Madagascar, from August 2016 to December 2017 and September 2018 to May 2020. We then compared this information to previous studies on captive infant development. Wild infant aye-ayes first emerged from the nest between two and three months old. Traveling between trees occurred between four and four and a half months old. First attempts at foraging for invertebrates in a woody substrate occurred between five and eight months. Though nursing was rarely observed, the event was witnessed as late as 17 months for one aye-aye. The earliest solo nesting occurred at 18 and a half months of age, and the latest at 23 months old. As with other primates, wild aye-ayes develop more slowly than their captive counterparts. We conclude that their protracted life history is likely associated with their percussive foraging behaviors and importance of invertebrates in their diet.

Variation in predicted COVID-19 risk among lemurs and lorises.

The novel coronavirus SARS‐CoV‐2, which in humans leads to the disease COVID‐19, has caused global disruption and more than 2 million fatalities since it first emerged in late 2019. As we write, infection rates are at their highest point globally and are rising extremely rapidly in some areas due to more infectious variants. The primary target of SARS‐CoV‐2 is the cellular receptor angiotensin‐converting enzyme‐2 (ACE2). Recent sequence analyses of the ACE2 gene predict that many nonhuman primates are also likely to be highly susceptible to infection. However, the anticipated risk is not equal across the Order. Furthermore, some taxonomic groups show high ACE2 amino acid conservation, while others exhibit high variability at this locus. As an example of the latter, analyses of strepsirrhine primate ACE2 sequences to date indicate large variation among lemurs and lorises compared to other primate clades despite low sampling effort. Here, we report ACE2 gene and protein sequences for 71 individual strepsirrhines, spanning 51 species and 19 genera. Our study reinforces previous results while finding additional variability in other strepsirrhine species, and suggests several clades of lemurs have high potential susceptibility to SARS‐CoV‐2 infection. Troublingly, some species, including the rare and endangered aye‐aye (Daubentonia madagascariensis), as well as those in the genera Avahi and Propithecus, may be at high risk. Given that lemurs are endemic to Madagascar and among the primates at highest risk of extinction globally, further understanding of the potential threat of COVID‐19 to their health should be a conservation priority. All feasible actions should be taken to limit their exposure to SARS‐CoV‐2.

To tell a different story: Unexpected diversity in local attitudes towards Endangered Aye‐ayes Daubentonia madagascariensis offers new opportunities for conservation

Abstract Human–wildlife interactions are usually centred on the conflict between local populations and species that are perceived as problematic. To better understand the human dimension, social science approaches are increasingly incorporated to delimit opportunities for coexistence and species conservation. Here we explore local attitudes and beliefs about one of these ‘problematic’ species, the Endangered Aye‐aye Daubentonia madagascariensis, the largest nocturnal primate on earth. We conducted a literature review on published beliefs and narratives about the Aye‐aye followed by 83 semi‐structured interviews in 11 villages in northeastern Madagascar. The Aye‐aye is generally perceived as a bad omen throughout its range. In many places it has to be killed on sight, while in others it is forbidden to be killed. We did not find any positive attitudes towards this species in the literature. However, this was not reflected by our interviews: although 47.0% of respondents held a negative attitude, more than half had a neutral or even positive attitude towards the Aye‐aye (36.1 and 18.1% respectively). Positive attitudes were linked to perceived pest control services on major cash crops. Negative attitudes are mostly related to the perception that when an Aye‐aye comes to a village, catastrophic things (e.g. deaths of community members) will happen, or that it destroys a village. These major narratives were mostly consistent within villages (79.5 ± 20.7% SD of respondents; range 50–100%) but considerably differed between villages. Negative attitudes towards the Aye‐aye were solely based on vague and generic narratives that are not reflected by its (true) ecology. Positive and neutral attitudes instead were related to observable behaviours benefitting people (i.e. pest control services) or curiosity about the species. This case study illustrates how even firm narratives can vary locally offering valuable starting points for targeted conservation or education programs. We therefore identified the Makira region of northeastern Madagascar as a potential stronghold for Aye‐aye conservation if specific actions highlighting its beneficial value could be initiated. In general, conservation practitioners should feel encouraged to look beyond the often told stories about ‘their’ target species and listen to local voices more often.

Pterygodermatites nycticebi infections in golden lion tamarins (Leontopithecus rosalia rosalia) and aye-ayes (Daubentonia madagascariensis) from a German zoo.

In a golden lion tamarin (Leontopithecus rosalia rosalia) colony kept indoors in a German zoo, two animals presented a sudden onset of reduced general condition, lethargy, and diarrhea. At animal capture for clinical examination, adult nematode stages were observed after stress-induced defecation. Despite treatment, two golden lion tamarins died in the following 2 days. At necropsy, spirurid stages were found in the lungs and intestine. Additionally, adult Pterygodermatites spp. were identified in histopathological samples of intestine and pancreas, confirming the previous diagnosis. Upon diagnosis, all animals were treated with ivermectin (0.2 mg/kg; SC). Thereafter, the general condition of the golden lion tamarins improved, whereby some of them excreted spirurid nematodes over 3 days. Four weeks after treatment, 20 fecal samples from the colony were examined and proved negative for parasitic stages. Given that common German cockroaches (Blattella germanica) are suitable intermediate hosts of Pterygodermatites nycticebi, 30 specimens were collected from seven different locations around the golden lion tamarins housing. Third-stage larvae of Pterygodermatites spp. were recovered from those cockroaches. Regular anthelmintic treatments, coprological screenings, and controls for intermediate hosts were recommended. More than 2 years later, P. nycticebi infection was diagnosed again histopathologically in an aye-aye (Daubentonia madagascariensis) which suddenly died. Coprological analysis confirmed the presence of spirurid eggs. Due to prosimian primates' cockroach-eating habits and given that total cockroach eradication proved impossible, continuous cockroach control strategies and regular treatments of primates are currently performed to prevent further P. nycticebi infections.

Home Range Size and Seasonal Variation in Habitat Use of Aye-Ayes (Daubentonia madagascariensis) in Torotorofotsy, Madagascar

Madagascar’s dramatic climatic fluctuations mean most lemurs adjust behaviors seasonally as resource availability fluctuates. Many lemurs will adopt one of two strategies, a resource maximizer or an area minimizer, when adjusting to seasonal shifts in resource availability. However, it is unknown if and how aye-aye (Daubentonia madagascariensis) ranging behavior is influenced by seasonality. We explored whether habitat use changed seasonally. We followed two aye-ayes, an adult male and an adult female, in the undisturbed forest of Torotorofotsy, Madagascar, from April 2012 to December 2017. We used instantaneous focal-animal sampling to collect behavioral data every 5 min and GPS locations every 20 min. We used the minimum convex polygon (MCP) to determine overall home range, and the Brownian bridge movement model (BBMM) to estimate overall and seasonal home range of the female aye-aye from November 2014 to October 2017. We used Wilcoxon signed-rank tests to determine whether there were significant differences in home range sizes between seasons across years and to examine whether there were seasonal differences in height of invertebrate foraging, generalized linear models to assess seasonal differences in travel rates and nesting locations, and χ² tests to determine whether there were differences in forest strata use when foraging on invertebrates. The male’s MCP home range was 2,586 ha, and the female’s MCP home range was 765 ha. The seasonal BBMM for the female varied between 443.6 and 1,010.0 ha, though infant rearing appears to have influenced these values. There were no significant differences in seasonal home range, travel rates, nesting locations, or height of invertebrate feeding. However, canopy level invertebrate foraging occurred more often than understory or ground levels. It appears aye-ayes in this undisturbed forest were not influenced by seasonal shifts and had larger home ranges than any previously reported. These findings may indicate that aye-ayes in an undisturbed forest are resource maximizers, closely linked to invertebrate assemblages.

The acoustic near-field measurement of aye-ayes’ biological auditory system utilizing a biomimetic robotic tap-scanning

The aye-aye (Daubentonia madagascariensis) is best known for its unique acoustic-based foraging behavior called ‘tap-scanning’ or ‘percussive foraging’. The tap-scanning is a unique behavior allowing aye-aye to locate small cavities beneath tree bark and extract wood-boring larvae from it. The tap-scanning requires the animal auditory system to have exceptional acoustic near-field sensitivity. This paper has experimentally investigated the effects of external pinna in the acoustic sensing and detection capabilities of aye-ayes. To experimentally evaluate the effects of external ear (pinna) of the aye-aye, the tap-scanning process was simulated using a robotic arm. A pinna was 3D printed using a CT scan obtained from a carcass. The pinna’s effect on the acoustic near-field has been evaluated in time and frequency domains for simulated tap-scanning with the pinna in upright and cupped positions. This idea originates from behavioral observations of the aye-aye using its ears in this way. The results suggest that the aye-aye can substantially enhance its acoustic near-field sensitivity through a cupped conformation during tap-scanning. Three phenomena contribute to this substantial enhancement of the acoustic near-field: (i) a considerable increase in the signal-to-noise ratio, (ii) the creation of a focal area and potentially a focal point to increase the spatial resolution, and (iii) an increase in the receiver peak frequency by changing near-field beam pattern for higher frequencies that can result in greater sensitivity due to a smaller wavelength.

Vascular Supply of Digit III and Foraging in the Aye‐Aye (Daubentonia madagascariensis)

The aye‐aye is an unusual primate that differs from other primates in several aspects of its anatomy and behavior. Its thin, elongated third digit serves as a tool for tap‐scanning and prey extraction during percussive foraging for wood‐boring insects. The surface temperature of digit III is higher than the other digits on the foraging hand; in contrast, digit III has a lower temperature than the other digits on the stabilizing hand and this difference has been hypothesized to relate to stenotic kinking of the palmar digital arteries during hyperextension at the metacarpophalangeal joint. Though previously described qualitatively, aye‐aye hand vasculature has never been photo‐documented or quantified. Here we describe and compare the arterial supply of the forearm and hand in Daubentonia madagascariensis and Lemur catta in the context of hand function during foraging.The forelimbs of two primates, one aye‐aye and one ring‐tailed lemur, were dissected and arterial morphology was documented and photographed. Measurements of palmar digital arteries were collected using a dissecting microscope equipped with an ocular reticle. Inter‐digit and inter‐species comparisons were made for the pattern and diameter of each vessel.Lemur catta and Daubentonia madagascariensis differ in several aspects of their forelimb vascular morphology. In L. catta, the brachial artery does not pass through the entepicondylar foramen and a superficial palmar arterial arch supplies the digits. By contrast, in D. madagascariensis the brachial artery does pass through the entepicondylar foramen and the palmar aspects of the digits are supplied by individual branches of the ulnar and radial arteries rather than an anastomotic arch. These two species also differ in terms of the diameter of the arteries leading to the digits relative to the diameter of the ulnar artery (as a way of assessing relative scale). In the aye‐aye, the arterial supply to digit III has the smallest relative diameter (digit IV has the largest). In the ring‐tailed lemur, digit V has the largest total relative diameter and digit I the smallest.These observed differences in the vascular supply of the forelimb and hand in Lemur catta and Daubentonia madagascariensis likely relate to differences in foraging and locomotor strategy. While it has been suggested that stenotic kinking is responsible for the relatively low temperature of digit III on the stabilizing hand in the aye‐aye, our study suggests that this temperature differential may instead be due to the relative under‐supply of this digit compared to the other digits of the hand.

Re-assessing the applicability of the Jarman/Bell model and Kay's threshold to the insectivorous aye-aye (Daubentonia madagascariensis).

Jarman/Bell principle and Kay's threshold suggest that large animals should not be able to sustain themselves on insects. However, animals with specialized morphological and/or behavioral adaptations violate these assumptions. Male aye-ayes were recently identified as having an insectivorous diet despite weighing 2.5 kg. We further explored this diet/body size disparity by studying behaviors of an adult female and juvenile male aye-aye. We collected behavioral data on an adult female and juvenile male aye-aye in Torotorofotsy, Madagascar from January 2016 to December 2017. We used instantaneous sampling to determine the frequency of feeding events and continuous sampling during feeding behaviors to assess duration of feeding bouts. Invertebrates comprised over 88% of the diet for both animals. A Wilcoxon signed-rank test found no significant difference in the female's feeding frequencies between the hot/rainy seasons and the cold/dry seasons. Our results support earlier findings that invertebrates are the aye-aye's main resource and corroborate that aye-ayes violate assumptions of the Jarman/Bell model and Kay's threshold. We suggest that the Jarman/Bell principle and Kay's threshold be used as supporting evidence and not to repudiate findings that do not conform to these guidelines.

DiceCT Analysis of the Extreme Gouging Adaptations Within the Masticatory Apparatus of the Aye-Aye (Daubentonia madagascariensis).

Relative to all other primates, the aye-aye (Daubentonia madagascariensis) exists at the extremes of both morphology and behavior. Its specialized anatomy-which includes hypselodont incisors and highly derived manual digits-reflects a dietary niche, unique among primates, which combines tap-foraging with gouging to locate and extract wood-boring larvae. Here, we explore the impact of this extreme dietary ecology upon the masticatory musculature of this taxon with reference to a second, similarly sized but highly generalist lemuriform-the mongoose lemur (Eulemur mongoz). Using non-destructive, high-resolution diffusible iodine-based contrast-enhanced computed tomography techniques, we reconstruct the three-dimensional volumes of eight masticatory muscles, and, for the first time in strepsirrhines, isolate and visualize their constituent muscle fascicles in situ and in three dimensions. Using these data, we report muscle volumes, forces, and fascicle lengths from each muscle portion, as well as their orientation relative to two standardized anatomical planes. Our findings demonstrate the overbuilt nature of the aye-aye's masticatory apparatus, in which each muscle possesses an absolutely and relatively larger muscle volume and PCSA than its counterpart in the mongoose lemur. Likewise, for several adductor muscles, aye-ayes also possess relatively greater fascicle lengths. Finally, we note several unusual features within the lateral pterygoid of the aye-aye-the muscle most responsible for jaw protrusion-that relate to force maximization and reorientation. As this jaw motion is critical to gouging, we interpret these differences to reflect highly specific specializations that facilitate the aye-aye's extreme subsistence strategy. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:282-294, 2020. © 2019 American Association for Anatomy.

A primate with a Panda's thumb: The anatomy of the pseudothumb of Daubentonia madagascariensis.

Accessory digits have evolved independently within several mammalian lineages. Most notable among these is the pseudothumb of the giant panda, which has long been considered one of the most extraordinary examples of contingent evolution. To date, no primate has been documented to possess such an adaptation. Here, we investigate the presence of this structure within the aye-aye (Daubentonia madagascariensis), a species renowned for several other specialized morphological adaptations in the hand, including a morphologically unique third digit. We combine physical dissection techniques with digital imaging processes across a sample of seven individuals (six adults and one immature individual) to describe and visualize the anatomy of the wrist and hand within the aye-aye. A distinct pseudothumb, which consists of both a bony component (an expanded radial sesamoid) and a dense cartilaginous extension (the "prepollex") was observed in all specimens. We demonstrate that this pseudodigit receives muscular attachments from three muscles, which collectively have the potential to enable abduction, adduction, and opposition. Finally, we demonstrate that the pseudothumb possesses its own distinct pad within the palm, complete with independent dermatoglyphs. Pseudothumbs have been suggested to improve palmar dexterity in taxa with overly -generalized first digits (e.g., pandas) and to widen the hand for digging (e.g., some fossorial moles), but the aye-aye's pseudothumb represents what we believe is a heretofore unrecognized third functional role: its accessory digit compensates for overspecialization of its fingers for non-gripping functions (in this case, the aye-aye's unique "tap foraging" practices).