Vocal learning-associated convergent evolution in mammalian proteins and regulatory elements.

Vocal production learning ("vocal learning") is a convergently evolved trait in vertebrates. To identify brain genomic elements associated with mammalian vocal learning, we integrated genomic, anatomical, and neurophysiological data from the Egyptian fruit bat (Rousettus aegyptiacus) with analyses of the genomes of 215 placental mammals. First, we identified a set of proteins evolving more slowly in vocal learners. Then, we discovered a vocal motor cortical region in the Egyptian fruit bat, an emergent vocal learner, and leveraged that knowledge to identify active cis-regulatory elements in the motor cortex of vocal learners. Machine learning methods applied to motor cortex open chromatin revealed 50 enhancers robustly associated with vocal learning whose activity tended to be lower in vocal learners. Our research implicates convergent losses of motor cortex regulatory elements in mammalian vocal learning evolution.

The effects of fossil taxa, hypothetical predicted ancestors, and a molecular scaffold on pseudoextinction analyses of extant placental orders.

Pseudoextinction analyses, which simulate extinction in extant taxa, use molecular phylogenetics to assess the accuracy of morphological phylogenetics. Previous pseudoextinction analyses have shown a failure of morphological phylogenetics to place some individual placental orders in the correct superordinal clade. Recent work suggests that the inclusion of hypothetical ancestors of extant placental clades, estimated by ancestral state reconstructions of morphological characters, may increase the accuracy of morphological phylogenetic analyses. However, these studies reconstructed direct hypothetical ancestors for each extant taxon based on a well-corroborated molecular phylogeny, which is not possible for extinct taxa that lack molecular data. It remains to be determined if pseudoextinct taxa, and by proxy extinct taxa, can be accurately placed when their immediate hypothetical ancestors are unknown. To investigate this, we employed molecular scaffolds with the largest available morphological data set for placental mammals. Each placental order was sequentially treated as pseudoextinct by exempting it from the molecular scaffold and recoding soft morphological characters as missing for all its constituent species. For each pseudoextinct data set, we omitted the pseudoextinct taxon and performed a parsimony ancestral state reconstruction to obtain hypothetical predicted ancestors. Each pseudoextinct order was then evaluated in seven parsimony analyses that employed combinations of fossil taxa, hypothetical predicted ancestors, and a molecular scaffold. In treatments that included fossils, hypothetical predicted ancestors, and a molecular scaffold, only 8 of 19 pseudoextinct placental orders (42%) retained the same interordinal placement as on the molecular scaffold. In treatments that included hypothetical predicted ancestors but not fossils or a scaffold, only four placental orders (21%) were recovered in positions that are congruent with the scaffold. These results indicate that hypothetical predicted ancestors do not increase the accuracy of pseudoextinct taxon placement when the immediate hypothetical ancestor of the taxon is unknown. Hypothetical predicted ancestors are not a panacea for morphological phylogenetics.

Sexual, allometric and forest cover effects on giant anteaters' movement ecology.

Knowing the influence of intrinsic and environmental traits on animals' movement is a central interest of ecology and can aid to enhance management decisions. The giant anteater (Myrmecophaga tridactyla) is a vulnerable mammal that presents low capacity for physiological thermoregulation and uses forests as thermal shelters. Here, we aim to provide reliable estimates of giant anteaters' movement patterns and home range size, as well as untangle the role of intrinsic and environmental drivers on their movement. We GPS-tracked 19 giant anteaters in Brazilian savannah. We used a continuous-time movement model to estimate their movement patterns (described by home range crossing time, daily distance moved and directionality), and provide an autocorrelated kernel density estimate of home range size. Then, we used mixed structural equations to integratively model the effects of sex, body mass and proportion of forest cover on movement patterns and home range size, considering the complex net of interactions between these variables. Male giant anteaters presented more intensive space use and larger home range than females with similar body mass, as it is expected in polygynous social mating systems. Males and females increased home range size with increasing body mass, but the allometric scaling of intensity of space use was negative for males and positive for females, indicating different strategies in search for resources. With decreasing proportion of forest cover inside their home ranges, and, consequently, decreasing thermal quality of their habitat, giant anteaters increased home range size, possibly to maximize the chances of accessing thermal shelters. As frequency and intensity of extreme weather events and deforestation are increasing, effective management efforts need to consider the role of forests as an important thermal resource driving spatial requirements of this species. We highlight that both intrinsic and environmental drivers of animal movement should be integrated to better guide management strategies.

Spermatic profile of captive giant anteaters (Myrmecophaga tridactyla): Knowing more to preserve better.

The giant anteater (Myrmecophaga tridactyla) is being threatened by natural habitat destruction and fragmentation, illegal hunting and road kills. In this context, the generation of basic information on the reproductive parameters of this species is vital, aiming to improve reproductive management via, amongst others, assisted reproductive technologies. This study aimed to describe the morphological and functional features of semen collected from captive giant anteaters. Electroejaculation was performed in 13 animals housed in zoos located in São Paulo state, Brazil. Semen samples were collected from 13 animals in 16 procedures. Samples were evaluated for volume, motility, vigor, pH, concentration, sperm morphology, and functional tests. The following mean values were obtained: volume 1.28 ± 0.27 mL; motility 28.3 ± 6.2%; vigor 2.4 ± 0.25; concentration 129.4 ± 36.1 × 106 sperm/mL; pH 7.4 ± 0.2. Total acrosome, head, midpiece, and tail sperm abnormalities were 3.2 ± 0.8%, 25.4 ± 3.6%, 20.7 ± 3.2%, and 14.7 ± 2.6%, respectively. Intact acrosome was found in 83.7 ± 3.1% and intact membrane in 81.1 ± 4.0% of all samples collected. Mitochondrial activity was 66.4 ± 6.0% (Class I), 18.7 ± 2.9% (Class II), 8.0 ± 2.0% (Class III), 3.9 ± 1.0% (Class IV), and 3.0 ± 0.9% (Class V). Sperm DNA fragmentation rate was 13.2 ± 3.7%. These results indicated that electroejaculation is a feasible method for semen collection in giant anteaters, allowing a more detailed description of the semen in this species.

Baby's best Foe-riend: Endogenous retroviruses and the evolution of eutherian reproduction.

High maternal investment in pregnancy and the perinatal period are prominent features of eutherian reproduction. Viviparity increases offspring survival, favoring high maternal prenatal investment. Matrotrophy through the placenta reduces maternal investment at early pregnancy, allowing the mother to abort embryos of subpar quality, therefore reducing resources wastage. On the other hand, intimate maternal-fetal interplay enables the fetus to manipulate maternal physiology to acquire more resources. This parent-offspring conflict likely drives the evolution of eutherian placentation, which is facilitated by the endogenous retroviruses (ERVs), ancient retroviruses that invaded host genome millions of years ago. ERVs bring new genes and novel regulatory elements into host genome, contribute to maternal-fetal tolerance, placenta-specific cell type formation, trophoblast gene expression network rewiring, and the establishment of imprinting. However, retroviruses/ERVs can function as infectious pathogens that interfere with host immune and inflammation pathways and cause genomic instability. In addition, ERVs coopted for host function may contribute to pathogenesis during infections due to their susceptibility to mechanisms activated by the invading pathogens. ERVs have been implicated in multiple perinatal adverse outcomes, therefore, eutherians must have evolved control mechanisms to regulate their function. Here we propose the TRIM family as an important participant of host antiviral defense and a likely candidate that mediates the coevolution of ERVs and their eutherian host. TRIMs have been shown to interact with retroviruses during each step of the infectious cycle. Understanding TRIMs' role in ERV regulation in the placenta may provide insight to both the physiology and pathology of eutherian reproduction.

Evolutionary transcriptomics implicates HAND2 in the origins of implantation and regulation of gestation length.

The developmental origins and evolutionary histories of cell types, tissues, and organs contribute to the ways in which their dysfunction produces disease. In mammals, the nature, development and evolution of maternal-fetal interactions likely influence diseases of pregnancy. Here we show genes that evolved expression at the maternal-fetal interface in Eutherian mammals play essential roles in the evolution of pregnancy and are associated with immunological disorders and preterm birth. Among these genes is HAND2, a transcription factor that suppresses estrogen signaling, a Eutherian innovation allowing blastocyst implantation. We found dynamic HAND2 expression in the decidua throughout the menstrual cycle and pregnancy, gradually decreasing to a low at term. HAND2 regulates a distinct set of genes in endometrial stromal fibroblasts including IL15, a cytokine also exhibiting dynamic expression throughout the menstrual cycle and gestation, promoting migration of natural killer cells and extravillous cytotrophoblasts. We demonstrate that HAND2 promoter loops to an enhancer containing SNPs implicated in birth weight and gestation length regulation. Collectively, these data connect HAND2 expression at the maternal-fetal interface with evolution of implantation and gestational regulation, and preterm birth.

Multivariate Analyses of the Activity Pattern and Behavior of the Lesser Anteater on Open and Closed Days at Córdoba Zoo, Argentina.

The human factor is one of the major determinants of animal welfare in zoos. Assessing changes in activity patterns, behavior and space use due to human presence might help understanding visitors' influence on these animal welfare indicators. In Córdoba (Argentina), we assessed the activity pattern and behavior of Tamandua tetradactyla (lesser anteaters; n = 5) during natural light/dark phases and the animals' use of space. We analyzed responses of lesser anteaters to humans in days open to the public (Sundays and Tuesdays) and days closed to the public (Mondays), collecting data at 5-minute intervals during 12 days, for each animal. Data were analyzed at two temporal scales: a 24 h period and visiting hours. Multivariate analyses showed no differences in activity pattern, behavior and space use among days, exhibiting a consistent response of each individual over the studied days. Principal Component Analysis showed differences between female and male behaviors. Based on these results, the visitor effect on these lesser anteaters would appear to be neutral, indicating that the presence of visitors is at most, a minor concern in the housing and management of these individuals in Córdoba Zoo.

Visitors' perceptions of zoo-housed lesser anteater (Tamandua tetradactyla) welfare: Observation plays a larger role than a brief informative talk.

There is a growing ethical concern in modern society about animals' quality of life. We hypothesize that zoo visitors' perception of zoo animal welfare, particularly in the case of lesser anteaters, changes positively after listening to scientific information. Visitors observing active lesser anteaters in their enclosures at Córdoba Zoo (Argentina) were asked to respond to a questionnaire about animal welfare. The treatment group (T) answered the questionnaire after listening to a brief informative talk based on local scientific studies on lesser anteaters. The control group (C) answered the questionnaire without hearing the informative talk. Visitors (87.2%) considered biological, sanitary, and sociocultural aspects to be necessary conditions for optimum wild zoo-housed animal welfare. The majority of visitors considered that natural surroundings provide the highest level of welfare for wild animals. Visitors in the T group ranked the zoo as providing a higher level of animal welfare than those in group C. In reference to management measurements, the T group agreed on the positive effect of the application of environmental enrichment (Likert Medians: C = 4 and T = 5; p = .0443). On the basis of their perception, most visitors in both groups stated that the lesser anteaters at Córdoba Zoo appeared to be in a good state of welfare. We interpret this as meaning that, what these Córdoba zoo visitors personally perceived while observing the lesser anteaters carried greater weight than what they learned from the informative talk, though the talk did slightly affect their opinion.

Reproductive behavior of the captive Sunda pangolin (Manis javanica Desmarest, 1822).

Understanding reproductive behavior is important for the conservation of endangered species, but research on the reproductive behavior of Sunda pangolins (Manis javanica Desmarest, 1822) is still very scarce. In this study, we used focal animal sampling and all-occurrence recording by an infrared monitor to observe the behaviors of two Sunda pangolins during a 5-day breeding period at the Pangolin Research Base for Artificial Rescue and Conservation Breeding of South China Normal University (PRB-SCNU). The behavioral characteristics and breeding strategies were analyzed, and the results were discussed together with information on other captive Sunda pangolin pairs at PRB-SCNU. The results found that there was no obvious estrus behavior in the captive female, while the male could exhibit sexual excitement and courtship behavior after a brief introduction period. Repeated copulation continued over many days after the female accepted the courtship. The average duration of copulatory behavior was 248.9 ± 148.7 s (n = 25), and all copulation occurred between 20:00 and 08:00 hr in the natural day-night photoperiod. The mating position of Sunda pangolins was lateral-ventral and was classified as the ninth or eleventh pattern under both Dewsbury's and Dixson's classification systems. This study can provide scientific guidance for the captive breeding and management of Sunda pangolins and other pangolin species, which is of great significance for ex situ conservation tactics.

Cooperative inflammation: The recruitment of inflammatory signaling in marsupial and eutherian pregnancy.

The evolution of viviparity in therian mammals, i.e. marsupials and "placental" mammals, occurred by retention of the conceptus in the female reproductive tract and precocious "hatching" from the shell coat. Both eutherian embryo implantation and the opossum embryo attachment reaction are evolutionarily derived from and homologous to a defensive inflammatory process induced after shell coat hatching. However, both lineages, marsupials and placental mammals, have modified the inflammatory response substantially. We review the induction, maintenance, and effects of inflammation throughout pregnancy, with special attention to the role of prostaglandins and the mucosal inflammatory response, both of which likely had roles in early mammalian viviparity. We propose that the key step was not only suppression of the inflammatory response after implantation in placental mammals, but also the transfer of the inflammatory cell-cell communication network to a different set of cell types than in generic inflammation. To support this conclusion we discuss evidence that pro-inflammatory signal production in the opossum is not limited to maternal cells, as expected in bona fide defensive inflammation, but also includes fetal tissues, in a process we term cooperative inflammation. The ways in which the inflammatory reaction was independently modified in these two lineages helps explain major life history differences between extant marsupials and eutherians.

Eutherian-Specific Gene TRIML2 Attenuates Inflammation in the Evolution of Placentation.

Evolution of highly invasive placentation in the stem lineage of eutherians and subsequent extension of pregnancy set eutherians apart from other mammals, that is, marsupials with short-lived placentas, and oviparous monotremes. Recent studies suggest that eutherian implantation evolved from marsupial attachment reaction, an inflammatory process induced by the direct contact of fetal placenta with maternal endometrium after the breakdown of the shell coat, and shortly before the onset of parturition. Unique to eutherians, a dramatic downregulation of inflammation after implantation prevents the onset of premature parturition, and is critical for the maintenance of gestation. This downregulation likely involved evolutionary changes on maternal as well as fetal/placental side. Tripartite-motif family-like2 (TRIML2) only exists in eutherian genomes and shows preferential expression in preimplantation embryos, and trophoblast-derived structures, such as chorion and placental disc. Comparative genomic evidence supports that TRIML2 originated from a gene duplication event in the stem lineage of Eutheria that also gave rise to eutherian TRIML1. Compared with TRIML1, TRIML2 lost the catalytic RING domain of E3 ligase. However, only TRIML2 is induced in human choriocarcinoma cell line JEG3 with poly(I:C) treatment to simulate inflammation during viral infection. Its knockdown increases the production of proinflammatory cytokines and reduces trophoblast survival during poly(I:C) stimulation, while its overexpression reduces proinflammatory cytokine production, supporting TRIML2's role as a regulatory inhibitor of the inflammatory pathways in trophoblasts. TRIML2's potential virus-interacting PRY/SPRY domain shows significant signature of selection, suggesting its contribution to the evolution of eutherian-specific inflammation regulation during placentation.

Solenodon genome reveals convergent evolution of venom in eulipotyphlan mammals.

Venom systems are key adaptations that have evolved throughout the tree of life and typically facilitate predation or defense. Despite venoms being model systems for studying a variety of evolutionary and physiological processes, many taxonomic groups remain understudied, including venomous mammals. Within the order Eulipotyphla, multiple shrew species and solenodons have oral venom systems. Despite morphological variation of their delivery systems, it remains unclear whether venom represents the ancestral state in this group or is the result of multiple independent origins. We investigated the origin and evolution of venom in eulipotyphlans by characterizing the venom system of the endangered Hispaniolan solenodon (Solenodon paradoxus). We constructed a genome to underpin proteomic identifications of solenodon venom toxins, before undertaking evolutionary analyses of those constituents, and functional assessments of the secreted venom. Our findings show that solenodon venom consists of multiple paralogous kallikrein 1 (KLK1) serine proteases, which cause hypotensive effects in vivo, and seem likely to have evolved to facilitate vertebrate prey capture. Comparative analyses provide convincing evidence that the oral venom systems of solenodons and shrews have evolved convergently, with the 4 independent origins of venom in eulipotyphlans outnumbering all other venom origins in mammals. We find that KLK1s have been independently coopted into the venom of shrews and solenodons following their divergence during the late Cretaceous, suggesting that evolutionary constraints may be acting on these genes. Consequently, our findings represent a striking example of convergent molecular evolution and demonstrate that distinct structural backgrounds can yield equivalent functions.

Land management strategies can increase oil palm plantation use by some terrestrial mammals in Colombia.

While the conservation role of remaining natural habitats in anthropogenic landscapes is clear, the degree to which agricultural matrices impose limitations to animal use is not well understood, but vital to assess species' resilience to land use change. Using an occupancy framework, we evaluated how oil palm plantations affect the occurrence and habitat use of terrestrial mammals in the Colombian Llanos. Further, we evaluated the effect of undergrowth vegetation and proximity to forest on habitat use within plantations. Most species exhibited restricted distributions across the study area, especially in oil palm plantations. Habitat type strongly influenced habitat use of four of the 12 more widely distributed species with oil palm negatively affecting species such as capybara and naked-tailed armadillo. The remaining species showed no apparent effect of habitat type, but oil palm and forest use probabilities varied among species. Overall, generalist mesocarnivores, white-tailed deer, and giant anteater were more likely to use oil palm while the remaining species, including ocelot and lesser anteater, showed preferences for forest. Distance to nearest forest had mixed effects on species habitat use, while understory vegetation facilitated the presence of species using oil palm. Our findings suggest that allowing undergrowth vegetation inside plantations and maintaining nearby riparian corridors would increase the likelihood of terrestrial mammals' occurrence within oil palm landscapes.

Hans Bluntschli in Berne: Researching reproduction in hedgehog tenrecs (Afrosoricida, Tenrecidae).

The Swiss anatomist Hans Bluntschli is best known as a primatologist. Yet, his focus during his later years in Berne was on reproduction in Malagasy tenrecs. This research was done with two graduate students, Robert Goetz and Fritz Strauss; all three had been obliged to leave Germany after the National Socialists came to power. Unique features of reproduction in tenrecs included nonantral follicles, intrafollicular fertilization, eversion of the corpus luteum, and polyovulation. The fertilized egg formed a blastula that developed into a blastocyst; there was no morula stage. A false placental cushion developed in the endometrium opposite the implantation site. Placentation was complex and included development of a prominent haemophagous organ. These findings are discussed in relation to current concepts of mammalian phylogeny that place tenrecs and golden moles in the same order and as close relatives to elephant shrews and the aardvark.

Evolutionary Tinkering of the Mandibular Canal Linked to Convergent Regression of Teeth in Placental Mammals.

Loss or reduction of teeth has occurred independently in all major clades of mammals [1]. This process is associated with specialized diets, such as myrmecophagy and filter feeding [2, 3], and led to an extensive rearrangement of the mandibular anatomy. The mandibular canal enables lower jaw innervation through the passage of the inferior alveolar nerve (IAN) [4, 5]. In order to innervate teeth, the IAN projects ascending branches directly through tooth roots [5, 6], bone trabeculae [6], or bone canaliculi (i.e., dorsal canaliculi) [7]. Here, we used micro-computed tomography (µ-CT) scans of mandibles, from eight myrmecophagous species with reduced dentition and 21 non-myrmecophages, to investigate the evolutionary fate of dental innervation structures following convergent tooth regression in mammals. Our observations provide strong evidence for a link between the presence of tooth loci and the development of dorsal canaliculi. Interestingly, toothless anteaters present dorsal canaliculi and preserve intact tooth innervation, while equally toothless pangolins do not. We show that the internal mandibular morphology of anteaters has a closer resemblance to that of baleen whales [7] than to pangolins. This is despite masticatory apparatus resemblances that have made anteaters and pangolins a textbook example of convergent evolution. Our results suggest that early tooth loci innervation [8] is required for maintaining the dorsal innervation of the mandible and underlines the dorsal canaliculi sensorial role in the context of mediolateral mandibular movements. This study presents a unique example of convergent redeployment of the tooth developmental pathway to a strictly sensorial function following tooth regression in anteaters and baleen whales.

Historical data for conservation: reconstructing range changes of Chinese pangolin (Manis pentadactyla) in eastern China (1970-2016).

The Chinese pangolin (Manis pentadactyla) has long suffered from intense exploitation driven by consumer demand for medicinal use and food. Effective conservation management is hampered by insufficient data on pangolin status and distribution. We integrated ecological niche modelling with long-term ecological records at the local scale (e.g. from local historical documents, grey and published literature and interviews) to estimate the magnitude of potential distribution change of the Chinese pangolin in eastern China (Fujian, Jiangxi and Zhejiang provinces) over time. Our results suggest that the range of the species decreased by 52.20% between the 1970s and early 2000s and that the population is now mainly confined to the Wuyi Mountains. This reduction in potential distribution range is attributable to anthropogenic pressures. According to our conservation prioritization analysis, the priority conservation area for the Chinese pangolin in eastern China is 51 268.4 km2, 5.62% of which is covered by nature reserves. There are 18 nature reserves and 46 prefectures which are priority areas for conservation in China. The priority-level nature reserves and prefectures in eastern China are mainly located in the centre of the Wuyi Mountains, and areas declared important tend to be around the Wuyi Mountains. We propose several actions to improve the conservation status of this species: establish or enlarge nature reserves, ensure local governments at the prefecture level prioritize conservation management and encourage local communities to participate in pangolin conservation.

The soft explosive model of placental mammal evolution.

BACKGROUND: Recent molecular dating estimates for placental mammals echo fossil inferences for an explosive interordinal diversification, but typically place this event some 10-20 million years earlier than the Paleocene fossils, among apparently more "primitive" mammal faunas. RESULTS: However, current models of molecular evolution do not adequately account for parallel rate changes, and result in dramatic divergence underestimates for large, long-lived mammals such as whales and hominids. Calibrating among these taxa shifts the rate model errors deeper in the tree, inflating interordinal divergence estimates. We employ simulations based on empirical rate variation, which show that this "error-shift inflation" can explain previous molecular dating overestimates relative to fossil inferences. Molecular dating accuracy is substantially improved in the simulations by focusing on calibrations for taxa that retain plesiomorphic life-history characteristics. Applying this strategy to the empirical data favours the soft explosive model of placental evolution, in line with traditional palaeontological interpretations - a few Cretaceous placental lineages give rise to a rapid interordinal diversification following the 66 Ma Cretaceous-Paleogene boundary mass extinction. CONCLUSIONS: Our soft explosive model for the diversification of placental mammals brings into agreement previously incongruous molecular, fossil, and ancestral life history estimates, and closely aligns with a growing consensus for a similar model for bird evolution. We show that recent criticism of the soft explosive model relies on ignoring both experimental controls and statistical confidence, as well as misrepresentation, and inconsistent interpretations of morphological phylogeny. More generally, we suggest that the evolutionary properties of adaptive radiations may leave current molecular dating methods susceptible to overestimating the timing of major diversification events.

Classics revisited: C. J. van der Horst on pregnancy and menstruation in elephant shrews.

BACKGROUND: Menstruation occurs only in higher primates, some bats, the spiny mouse and the elephant shrew. Our knowledge of the latter species is due to work by C. J. van der Horst. FINDINGS: Changes in the uterine stroma are initially similar in fertile and infertile cycles and are confined to a small area. In pregnant animals, the presence of the conceptus causes further development to an implantation chamber. In infertile cycles an outgrowth of highly glandular stroma (a polyp) appears. With decline of the corpora lutea it is shed in a process equivalent to menstruation. Van der Horst described the further development of the placenta and a decidua pseudocapsularis in pregnant animals. In addition he built a unique collection that has thrown light on embryonic development and placentation in other South African mammals. CONCLUSIONS: The changes in endometrial stromal cells during the menstrual cycle appear similar between primates and the elephant shrew and deserve to be studied at the molecular level.

On the presence and absence of suckling order in polytocous mammals.

Mammals have developed a variety of suckling behaviours ranging from tenacious nipple attachment in some rodents and marsupials to once-a-day suckling in rabbit. However, a common feature of suckling that was found in many mammals is the suckling order, or a partial preference to suckle a particular teat (teat fidelity) or part of the udder (suckling preference). A lack of suckling order is observed only in a few mammals. In this article, the possible background of the presence or absence of suckling order in eutherian polytocous mammals is discussed either from the maternal investment or sibling competition point of view. Characteristics related to maternal investment in species in which the suckling order has already been studied at least partially, were classified using C4.5 algorithm (J48 classifier in Weka 3.8.1), and decision tree was built. In the context of sibling competition, an extensive form game (game theory) was predicted to show the optimal suckling strategy considering the basic relations among littermates in two situations (littermates of equal strength/dominance and littermates with different strength/dominance). Although no ultimate conclusion can be drawn, it appears that the suckling order is typical for species whose reproductive system requires a lower maternal investment (up to one litter/year, monogamy, biparental care, lower litter birth weight); and, it appears that the suckling order is inherent to the weaker (inferior) siblings.

Rates of Molecular Evolution Suggest Natural History of Life History Traits and a Post-K-Pg Nocturnal Bottleneck of Placentals.

Life history and behavioral traits are often difficult to discern from the fossil record, but evolutionary rates of genes and their changes over time can be inferred from extant genomic data. Under the neutral theory, molecular evolutionary rate is a product of mutation rate and the proportion of neutral mutations [1, 2]. Mutation rates may be shared across the genome, whereas proportions of neutral mutations vary among genes because functional constraints vary. By analyzing evolutionary rates of 1,185 genes in a phylogeny of 89 mammals, we extracted historical profiles of functional constraints on these rates in the form of gene-branch interactions. By applying a novel statistical approach to these profiles, we reconstructed the history of ten discrete traits related to activity, diet, and social behaviors. Our results indicate that the ancestor of placental mammals was solitary, seasonally breeding, insectivorous, and likely nocturnal. The results suggest placental diversification began 10-20 million years before the K-Pg boundary (66 million years ago), with some ancestors of extant placental mammals becoming diurnal and adapted to different diets. However, from the Paleocene to the Eocene-Oligocene transition (EOT, 33.9 mya), we detect a post-K-Pg nocturnal bottleneck where all ancestral lineages of extant placentals were nocturnal. Although diurnal placentals may have existed during the elevated global temperatures of the Paleocene-Eocene thermal maximum [3], we hypothesize that diurnal placentals were selectively extirpated during or after the global cooling of the EOT, whereas some nocturnal lineages survived due to preadaptations to cold environments [4].