Maria Sagot

Effects of roost specialization on extinction risk in bats

Understanding causes and consequences of ecological specialization is of major concern in conservation. Specialist species are particularly vulnerable to human activities. If their food or habitats are depleted or lost, they may not be able to exploit alternative resources, and population losses may result. We examined International Union for Conservation of Nature (IUCN) Red List bat data and the number of roosts used per species (accounting for phylogenetic independence) to determine whether roost specialization is correlated with extinction risk. We found a significant correlation between the IUCN Red List category and the number of roost types used. Species that use fewer roost types had a higher risk of extinction. We found that caves and similar structures were the most widely used roost types, particularly by species under some level of risk of extinction. Many critically endangered, endangered, or vulnerable species used natural roosts exclusively, whereas less threatened species used natural and human-made roosts. Our results suggest that roost loss, particularly in species that rely on a single roost type, may be linked to extinction risk. Our focus on a single life history trait prevented us from determining how important this variable is for extinction risk relative to other variables, but we have taken a first step toward prioritizing conservation actions. Our results also suggest that roost specialization may exacerbate population declines due to other risk factors, such as hunting pressure or habitat loss, and thus that management actions to preserve species under risk of extinction should prioritize protection of roosting sites.

Social calls produced within and near the roost in two species of tent-making bats, Dermanura watsoni and Ectophylla alba.

Social animals regularly face the problem of relocating conspecifics when separated. Communication is one of the most important mechanisms facilitating group formation and cohesion. Known as contact calls, signals exchanged between conspecifics that permit group maintenance are widespread across many taxa. Foliage-roosting bats are an excellent model system for studying the evolution of contact calling, as there are opportunities to compare closely related species that exhibit major differences in ecology and behavior. Further, foliage-roosting bats rely on relatively ephemeral roosts, which leads to major challenges in maintaining group cohesion. Here, we report findings on the communication signals produced by two tent-making bats, Dermanura watsoni and Ectophylla alba. We found that both species produced calls in the early morning near the roost that were associated with roostmate recruitment. Calling often ended once other bats arrived at the tent, suggesting that calls may be involved in roostmate recruitment and group formation. The structure and function of these calls are described and future research directions are discussed.

Human-modified habitats change patterns of population genetic structure and group relatedness in Peter's tent-roosting bats.

Abstract Although coloniality is widespread among mammals, it is still not clear what factors influence composition of social groups. As animals need to adapt to multiple habitat and environmental conditions throughout their range, variation in group composition should be influenced by adaptive adjustment to different ecological factors. Relevant to anthropogenic disturbance, increased habitat modification by humans can alter species’ presence, density, and population structure. Therefore, it is important to understand the consequences of changes to landscape composition, in particular how habitat modification affects social structure of group‐forming organisms. Here, we combine information on roosting associations with genetic structure of Peters tent‐roosting bats, Uroderma bilobatum to address how different habitat characteristics at different scales affect structure of social groups. By dividing analyses by age and sex, we determined that genetic structure was greater for adult females than adult males or offspring. Habitat variables explained 80% of the variation in group relatedness (mainly influenced by female relatedness) with roost characteristics contributing the most explained variation. This suggests that females using roosts of specific characteristics exhibit higher relatedness and seem to be philopatric. These females mate with more males than do more labile female groups. Results describe ecological and microevolutionary processes, which affect relatedness and social structure; findings are highly relevant to species distributions in both natural and human‐modified environments.

Same-sex courtship behaviors in male-biased populations: evidence for the mistaken identity hypothesis

Same-sex sexual behaviors (SSSB) have been recorded in nearly all major animal groups and are often found in populations with skewed sex ratios (SR). Here, we study the role of sex ratios in the frequency of SSSB to better understand the conditions that give rise to such puzzling behaviors. We observed SSSB in multiple populations of the common fruit fly (Drosophila melanogaster) after manipulation of sex ratios. We also recorded male responses after being pursued by other males. We found more male-male sexual interactions in male-biased populations and a significant decrease of these behaviors after consecutive days of observation. Males pursued by other males reacted to such encounters. Our results provide support for the mistaken identity hypothesis, in which males are unable to differentiate between sexes at first encounter. With this work, we help elucidate possible social conditions that facilitate the appearance of such intriguing behaviors in nature.

Development and characterization of seventeen microsatellite loci for the Peter’s tent-roosting bat ( Uroderma bilobatum )

In the Neotropics, Peter’s tent-roosting bat (Uroderma bilobatum) is an important keystone species. U. bilobatum promotes plant community diversity and secondary succession, and is becoming more abundant in human-modified habitats where it roosts in non-native plants. Although this change in roosting preferences can have detrimental consequences to their populations, to date, no study has quantified this phenomenon from a population genetic perspective. To investigate effect of human-modified habitats on group cohesion, population structure, and genetic diversity, we developed and characterized 17 microsatellite loci. Primer pairs were screened on 187 individuals from 12 different social groups. Levels of polymorphism ranged from 3 to 14 alleles. Of the 17 loci, 3 revealed significant departures from Hardy–Weinberg equilibrium and evidence of null alleles. Use of these markers will allow researchers to understand effects to population genetic structure and diversity due to changes in habitat use, which is important information to form the best correct management strategy and to ensure perpetuity of an important seed disperser.

Effects of Temperature and Day Length on Daily Movements and Home Range of Glaucomys volans (Southern Flying Squirrel) in the Northeastern United States

Abstract To maximize energy gained and minimize energy expended, animals should forage in a manner that gives them the largest benefit at the lowest cost. Species living in seasonal environments in the northeastern US, such as the Glaucomys volans (Southern Flying Squirrel), need to overcome high energetic demands associated with thermoregulation and food availability. In this study, we measured nightly travelled distance and home range of Southern Flying Squirrel to understand how they adapt to changes in temperature and day length. Our results showed that Southern Flying Squirrel travelled longer distances and expanded their home range in warmer temperatures and longer day-lengths. Our study contributes to our understanding of how animals adapt to constantly changing environmental conditions in the northeastern United States.

Geographic variation of contact calls suggest distinct modes of vocal transmission in a leaf-roosting bat

Populations that have historically been isolated from each other are expected to differ in some heritable features. This divergence could be due to drift (and other mechanisms of neutral evolution) or differential adaptation of populations to local conditions. Discriminating between these two evolutionary trajectories can be difficult, but when possible, such data provides critical insight into the evolutionary history of a species. Here, we examine the patterns of geographic variation of two contact signals regularly produced by disc-winged bats, Thyroptera tricolor, and discuss possible processes leading to the observed patterns of differentiation. We compared allopatric populations separated by an elevational barrier, and estimated genetic distance using nuclear microsatellite loci. Our findings revealed that the mountain ridge is permeable to gene flow. Acoustic divergence was significantly explained by genetic and spatial factors, supporting the notion that stochastic factors are the main drivers of signal divergence. Yet, we found different patterns of geographic variation between the two types of calls. We examine how this variability in the patterns of acoustic divergence may suggest distinct modes of signal transmission within and between populations (i.e., social vs genetic transmission). This work provides further support of the role of random change shaping communication systems in mammals, and highlights the importance of studying multiple elements of a species repertoire to evaluate the underlying processes driving signal evolution.Significance statementDespite increasing interest in studying patterns of acoustic divergence, the relative contribution of adaptive and stochastic processes underlying variation of acoustic signals remain poorly understood, particularly in mammals. Our study examines signal divergence in Spix’s disc-winged bats, Thyoptera tricolor, with the goal of understanding the underlying processes driving signal evolution. Specifically, we studied whether the patterns of geographic variation of two social signals regularly emitted by T. tricolor are congruent with patterns of genetic distance among populations separated by a geographic barrier. We demonstrate that genetic and spatial distance explains acoustic variation, which points to stochastic processes as major drivers of signal divergence in T. tricolor. Notably, we found that the patterns of geographic variation differ between the two types of calls studied. We suggest that this variation results from distinct modes of vocal transmission within populations. Comparison of different signal types provides additional insight of social pressures shaping call design.

Effects of Range, Habitat and Roosting Ecology in Patterns of Group Association in Bats

There is a wide variety of ecological factors that can potentially act as selective pressures driving the evolution of social behavior in bats. For instance, many behavioral ecologists recognize a relationship between social behavior, geographic distribution, and variation in resource abundance and distribution. Moreover, some bat species can use preexisting roosts such as tree cavities and caves, while others are able to modify nests, burrows, or foliage to create their own shelters. Thus, it is not surprising that the diverse social interactions found in bats have also been attributed to lifespan, availability, and distribution of roost sites. Here, I aim to determine if roost lifespan, number of roosts used and/or range size are important determinants of group stability. I conducted a literature review to collect information on group stability, roost lifespan, number or roosts used and range size, and I tested for correlated evolution between these variables. I found that roost lifespan, number of roosts and range size did not predict group stability. However, there was an association between range size and number of roosts used. Species with wider ranges encounter diverse habitats, environmental conditions, and roost types with different lifespans. Thus, it is not surprising that bats modify their social structure to adapt to these specific local conditions. Studying how different ecological characteristics interact to produce differences in group stability, provide the basis for understanding the complex route to sociality.

Noteworthy record of Crawford's desert shrew (Notiosorex crawfordi) from southern Nevada

Abstract We review the known records of desert shrews from Nevada and report the results of genetic analyses of a specimen from Ash Meadows National Wildlife Refuge, Nye County, Nevada, which help clarify the evolutionary relationships of the genus Notiosorex from southwestern United States.