-
Ecology and Evolution Jul 2023Madagascar exhibits exceptionally high levels of biodiversity and endemism. Models to explain the diversification and distribution of species in Madagascar stress the...
Madagascar exhibits exceptionally high levels of biodiversity and endemism. Models to explain the diversification and distribution of species in Madagascar stress the importance of historical variability in climate conditions which may have led to the formation of geographic barriers by changing water and habitat availability. The relative importance of these models for the diversification of the various forest-adapted taxa of Madagascar has yet to be understood. Here, we reconstructed the phylogeographic history of Gerp's mouse lemur () to identify relevant mechanisms and drivers of diversification in Madagascar's humid rainforests. We used restriction site associated DNA (RAD) markers and applied population genomic and coalescent-based techniques to estimate genetic diversity, population structure, gene flow and divergence times among populations and its two sister species and . Genomic results were complemented with ecological niche models to better understand the relative barrier function of rivers and altitude. We show that diversified during the late Pleistocene. The inferred ecological niche, patterns of gene flow and genetic differentiation in suggest that the potential for rivers to act as biogeographic barriers depended on both size and elevation of headwaters. Populations on opposite sides of the largest river in the area with headwaters that extend far into the highlands show particularly high genetic differentiation, whereas rivers with lower elevation headwaters have weaker barrier functions, indicated by higher migration rates and admixture. We conclude that likely diversified through repeated cycles of dispersal punctuated by isolation to refugia as a result of paleoclimatic fluctuations during the Pleistocene. We argue that this diversification scenario serves as a model of diversification for other rainforest taxa that are similarly limited by geographic factors. In addition, we highlight conservation implications for this critically endangered species, which faces extreme habitat loss and fragmentation.
PubMed: 37408627
DOI: 10.1002/ece3.10254 -
Folia Primatologica; International... Oct 2023The choice of behavioral sampling method can impact the outcome of data collection, however, few direct comparisons between methods have been made. We compared the...
The choice of behavioral sampling method can impact the outcome of data collection, however, few direct comparisons between methods have been made. We compared the performance of instantaneous group scan sampling (scan sampling) and focal continuous sampling with variable session durations (focal sampling) in estimating activity patterns, diet composition, and spatial proximity in seven groups of wild coppery titi monkeys (Plecturocebus cupreus) in Peruvian Amazonia. We used a series of paired samples Wilcoxon tests to compare daily proportions of time allocated to each type of activity/food/proximity category in each sampling method. In addition, we compared our results with those of other studies conducted on the same population of titi monkeys at other times. Focal sampling provided significantly lower estimates for moving time and significantly higher estimates for resting time compared to scan sampling, likely because scan sampling tends to give higher estimates of more conspicuous behaviors and lower estimates of less conspicuous behaviors. For diet composition, scan sampling gave similar results to other studies, while focal sampling gave significantly lower estimates for feeding on fruits and higher estimates for feeding on arthropods. The most likely reason is that focal sampling with variable session durations tends to overestimate behaviors during which a focal animal is less likely to go out of view, such as feeding on arthropods in the lower strata of the forest. Our results suggest that a pilot study comparing different methods should be conducted prior to collecting data, as not all methods are interchangeable.
Topics: Animals; Callicebus; Pilot Projects; Diet; Feeding Behavior; Fruit; Arthropods
PubMed: 38593409
DOI: 10.1163/14219980-bja10016 -
American Journal of Biological... Jan 2024The investigation of morphological variation in animals is widely used in taxonomy, ecology, and evolution. Using large datasets for meta-analyses has dramatically...
Morphological variability or inter-observer bias? A methodological toolkit to improve data quality of multi-researcher datasets for the analysis of morphological variation.
OBJECTIVES
The investigation of morphological variation in animals is widely used in taxonomy, ecology, and evolution. Using large datasets for meta-analyses has dramatically increased, raising concerns about dataset compatibilities and biases introduced by contributions of multiple researchers.
MATERIALS AND METHODS
We compiled morphological data on 13 variables for 3073 individual mouse lemurs (Cheirogaleidae, Microcebus spp.) from 25 taxa and 153 different sampling locations, measured by 48 different researchers. We introduced and applied a filtering pipeline and quantified improvements in data quality (Shapiro-Francia statistic, skewness, and excess kurtosis). The filtered dataset was then used to test for genus-wide sexual size dimorphism and the applicability of Rensch's, Allen's, and Bergmann's rules.
RESULTS
Our pipeline reduced inter-observer bias (i.e., increased normality of data distributions). Inter-observer reliability of measurements was notably variable, highlighting the need to reduce data collection biases. Although subtle, we found a consistent pattern of sexual size dimorphism across Microcebus, with females being the larger (but not heavier) sex. Sexual size dimorphism was isometric, providing no support for Rensch's rule. Variations in tail length but not in ear size were consistent with the predictions of Allen's rule. Body mass and length followed a pattern contrary to predictions of Bergmann's rule.
DISCUSSION
We highlighted the usefulness of large multi-researcher datasets for testing ecological hypotheses after correcting for inter-observer biases. Using genus-wide tests, we outlined generalizable patterns of morphological variability across all mouse lemurs. This new methodological toolkit aims to facilitate future large-scale morphological comparisons for a wide range of taxa and applications.
Topics: Animals; Female; Humans; Body Size; Cheirogaleidae; Observer Variation; Data Accuracy; Reproducibility of Results
PubMed: 37607125
DOI: 10.1002/ajpa.24836 -
The Journal of Experimental Biology Jul 2023Atta leaf-cutter ants are the prime herbivore in the Neotropics: differently sized foragers harvest plant material to grow a fungus as a crop. Efficient foraging...
Atta leaf-cutter ants are the prime herbivore in the Neotropics: differently sized foragers harvest plant material to grow a fungus as a crop. Efficient foraging involves complex interactions between worker size, task preferences and plant-fungus suitability; it is, however, ultimately constrained by the ability of differently sized workers to generate forces large enough to cut vegetation. In order to quantify this ability, we measured bite forces of Atta vollenweideri leaf-cutter ants spanning more than one order of magnitude in body mass. Maximum bite force scaled almost in direct proportion to mass; the largest workers generated peak bite forces 2.5 times higher than expected from isometry. This remarkable positive allometry can be explained via a biomechanical model that links bite forces with substantial size-specific changes in the morphology of the musculoskeletal bite apparatus. In addition to these morphological changes, we show that bite forces of smaller ants peak at larger mandibular opening angles, suggesting a size-dependent physiological adaptation, probably reflecting the need to cut leaves with a thickness that corresponds to a larger fraction of the maximum possible gape. Via direct comparison of maximum bite forces with leaf mechanical properties, we demonstrate (i) that bite forces in leaf-cutter ants need to be exceptionally large compared with body mass to enable them to cut leaves; and (ii), that the positive allometry enables colonies to forage on a wider range of plant species without the need for extreme investment in even larger workers. Our results thus provide strong quantitative arguments for the adaptive value of a positively allometric bite force.
Topics: Animals; Ants; Bite Force; Mandible; Herbivory; Plant Leaves
PubMed: 37293932
DOI: 10.1242/jeb.245140 -
Journal of Invertebrate Pathology Feb 2024Social insects, such as ants, are preferred host organisms of pathogens and parasites because colonies are densely populated, and the number of potential hosts is high...
Social insects, such as ants, are preferred host organisms of pathogens and parasites because colonies are densely populated, and the number of potential hosts is high in the same place and time. Within a colony, individuals are exposed differentially to risks according to their function and age. Thus, older individuals forage and are therefore the most exposed to infection, predation, or physical stress, while young workers mostly stay inside the sheltered nest being less exposed. Immune investment is considered to be dependent on an individual's age and pathogen pressure. Long-term exposure to a parasite could affect the immune activity of individuals in an intriguing way that interferes with the age-dependent decline in immunocompetence. However, there are only few cases in which such interferences can be studied. The myrmecopathogenic fungus Rickia wasmannii, which infects entire colonies without killing the workers, is a suitable candidate for such studies. We investigated the general immunocompetence of Myrmica scabrinodis ant workers associated with non-lethal fungal infection by measuring the levels of active phenoloxidase (PO) and total PO (PPO) (reflecting the amount of both active and inactive forms of the enzyme) in two age classes. The level of PO proved to be higher in infected workers than in uninfected ones, while the level of PPO increased with age but was not affected by infection. Overall, these results indicate that a long-term infection could go hand in hand with increased immune activity of ant workers, conferring them higher level of protection.
Topics: Animals; Parasites; Ants; Mycoses; Predatory Behavior; Stress, Physiological
PubMed: 38042446
DOI: 10.1016/j.jip.2023.108027 -
Ecology and Evolution Apr 2024Ants are crucial ecosystem engineers, and their ecological success is facilitated by a division of labour among sterile "workers". In some ant lineages, workers have...
Ants are crucial ecosystem engineers, and their ecological success is facilitated by a division of labour among sterile "workers". In some ant lineages, workers have undergone further morphological differentiation, resulting in differences in body size, shape, or both. Distinguishing between changes in size and shape is not trivial. Traditional approaches based on allometry reduce complex 3D shapes into simple linear, areal, or volume metrics; modern approaches using geometric morphometrics typically rely on landmarks, introducing observer bias and a trade-off between effort and accuracy. Here, we use a landmark-free method based on large deformation diffeomorphic metric mapping (LDDMM) to assess the co-variation of size and 3D shape in the mandibles and head capsules of leaf-cutter ants, a species exhibiting extreme worker size-variation. Body mass varied by more than two orders of magnitude, but a shape atlas created via LDDMM on μ-CT-derived 3D mesh files revealed only two distinct head capsule and mandibles shapes-one for the minims (body mass < 1 mg) and one for all other workers. We discuss the functional significance of the identified 3D shape variation, and its implications for the evolution of extreme polymorphism in .
PubMed: 38633523
DOI: 10.1002/ece3.11236 -
Journal of Chemical Ecology Mar 2024Bumble bees are important pollinators in natural environments and agricultural farmlands, and they are in particular adapted to harsh environments like high mountain...
Bumble bees are important pollinators in natural environments and agricultural farmlands, and they are in particular adapted to harsh environments like high mountain habitats. In these environments, animals are exposed to low temperature and face the risk of desiccation. The Eastern Himalayas are one of the recognized biodiversity hotspots worldwide. The area covers subtropical rainforest with warm temperature and high precipitation as well as high mountain ranges with peaks reaching up to 7,000 m, shaping a diverse floral and faunal community at the different elevational zones. To identify possible adaptation strategies, we investigated the cuticular hydrocarbon profiles of four bumble bee species occurring at different elevational ranges in Arunachal Pradesh, the northeastern most state in India. At 17 locations along an elevational gradient, we collected workers of two species from lower elevations (B. albopleuralis and B. breviceps; ~ 100 m - 3,000 m asl) and two species from higher elevations (B. prshewalskyi and B. mirus; ~ 2,800 m - 4,500 m asl). The CHC profiles of all four species showed a significant degree of variation in the composition of hydrocarbons, indicating species specificity. We also found clear correlation with elevation. The weighted mean chain length of the hydrocarbons significantly differed between the low and high elevation species, and the proportion of saturated hydrocarbons in CHC profiles significantly increased with the elevational range of the bumble bee species. Our results indicate that bumble bees living at high elevations reduce the risk of water loss by adapting their CHC composition on their cuticle, a phenomenon that has also been found in other insects like ants and fruit flies.
PubMed: 38470528
DOI: 10.1007/s10886-024-01486-x -
Primates; Journal of Primatology Mar 2024Birth is a fundamental event in the life of animals, including our own species. More reports of wild non-human primate births and stillbirths are thus needed to better...
Birth is a fundamental event in the life of animals, including our own species. More reports of wild non-human primate births and stillbirths are thus needed to better understand the evolutionary pressures shaping parturition behaviors in our lineage. In diurnal non-human primates, births generally occur at night, when individuals are resting. Consequently, they are difficult to observe in the wild and most of the current knowledge regarding perinatal behaviors comes from rare daytime births. Information about stillbirths is even rarer and their proximate causes are generally unknown. Here, we present detailed observations of a daytime birth of a stillborn wild mandrill (Mandrillus sphinx). During this event, which lasted an entire day, we recorded the behaviors of the parturient female ad libitum, using video recordings and photos. The 5-year-old female was primiparous and of low dominance rank. The length of her pregnancy was shorter than usual and the partum phase was extremely long compared to other birth reports in non-human primates. The female disappeared shortly after this event and was assumed to have died. We discuss the possible causes of this stillbirth including the infant's presentation at birth and maternal inexperience.
Topics: Humans; Pregnancy; Animals; Female; Mandrillus; Stillbirth; Parturition; Biological Evolution
PubMed: 38133716
DOI: 10.1007/s10329-023-01112-6 -
Learning & Behavior Mar 2024Desert ant foragers are well known for their visual navigation abilities, relying on visual cues in the environment to find their way along routes back to the nest. If...
Desert ant foragers are well known for their visual navigation abilities, relying on visual cues in the environment to find their way along routes back to the nest. If the inconspicuous nest entrance is missed, ants engage in a highly structured systematic search until it is discovered. Searching ants continue to be guided by visual cues surrounding the nest, from which they derive a location estimate. The precision level of this estimate depends on the information content of the nest panorama. This study examines whether search precision is also affected by the directional distribution of visual information. The systematic searching behavior of ants is examined under laboratory settings. Two different visual scenarios are compared - a balanced one where visual information is evenly distributed, and an unbalanced one where all visual information is located on one side of an experimental arena. The identity and number of visual objects is similar over both conditions. The ants search with comparable precision in both conditions. Even in the visually unbalanced condition, searches are characterized by balanced precision on both sides of the arena. This finding lends support to the idea that ants memorize the visual scenery at the nest as panoramic views from different locations. A searching ant is thus able to estimate its location with equal precision in all directions, leading to symmetrical search paths.
Topics: Animals; Cues; Ants; Homing Behavior; Appetitive Behavior
PubMed: 37985604
DOI: 10.3758/s13420-023-00613-0 -
Philosophical Transactions of the Royal... Jul 2024Many animals use formalized signals to communicate dominance relationships. In some primates, such as macaques, the function of such signals varies with dominance style....
Many animals use formalized signals to communicate dominance relationships. In some primates, such as macaques, the function of such signals varies with dominance style. Despotic species produce unidirectional submission signals that have a dual function: in conflict contexts, they signal a willingness to withdraw, whereas in peaceful contexts, they indicate the agreement to subordination. More despotic species produce these calls to a lesser extent than less despotic species. Here, we investigated whether the use of unidirectional submission signals is also related to dominance style in two lemur species and whether signalling subordination stabilizes social relationships at the group level. Ring-tailed lemurs () exhibit a more despotic dominance hierarchy than Verreaux's sifakas (). We observed social interactions in 75 dyads of Verreaux's sifakas and 118 dyads of ring-tailed lemurs. Both species used unidirectional submissive calls that have a dual function, potentially suggesting convergent evolution of the function of these signals in independent primate lineages. However, signalling subordination did not stabilize social relationships at the group level in both species. Additionally, subordination occurred more frequently in dyads of the more despotic ring-tailed lemurs than in Verreaux's sifakas, indicating opposite patterns to macaques in the coevolution of social traits with dominance style. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.
Topics: Animals; Vocalization, Animal; Lemur; Social Dominance; Male; Female; Madagascar; Species Specificity; Animal Communication; Dominance-Subordination
PubMed: 38768209
DOI: 10.1098/rstb.2023.0197