Sex-Specific Correlations of Individual Heterozygosity, Parasite Load, and Scalation Asymmetry in a Sexually Dichromatic Lizard

Heterozygosity-fitness correlations (HFCs) provide insights into the genetic bases of individual fitness variation in natural populations. However, despite decades of study, the biological significance of HFCs is still under debate. In this study, we investigated HFCs in a large population of the sexually dimorphic lizard Takydromus viridipunctatus (Lacertidae). Because of the high prevalence of parasitism from trombiculid mites in this lizard, we expect individual fitness (i.e., survival) to decrease with increasing parasite load. Furthermore, because morphological asymmetry is likely to influence individuals\u27 mobility (i.e., limb asymmetry) and male biting ability during copulation (i.e., head asymmetry) in this species, we also hypothesize that individual fitness should decrease with increasing morphological asymmetry. Although we did not formally test the relationship between morphological asymmetry and fitness in this lizard, we demonstrated that survival decreased with increasing parasite load using a capture-mark-recapture data set. We used a separate sample of 140 lizards to test the correlations between individual heterozygosity (i.e., standardized mean d2 and HL based on 10 microsatellite loci) and the two fitness traits (i.e., parasite load and morphological asymmetry). We also evaluated and excluded the possibility that single-locus effects produced spurious HFCs. Our results suggest male-only, negative correlations between individual heterozygosity and parasite load and between individual heterozygosity and asymmetry, suggesting sex-specific, positive HFCs. Male T. viridipunctatus with higher heterozygosity tend to have lower parasite loads (i.e., higher survival) and lower asymmetry, providing a rare example of HFC in reptiles

COMPARATIVE GENETICS OF APODEMUS AGRARIUS (RODENTIA: MAMMALIA) FROM INSULAR AND CONTINENTAL EURASIAN POPULATIONS: CYTOCHROME B SEQUENCE ANALYSES

To reexamine genetic divergence of Apodemus agrarius in insular Taiwan and the Korean Jeju from other populations in continental Eurasia, we obtained 91 cytochrome b complete sequences of A. agrarius across Eurasia, and these sequences were compared to eight corresponding sequences of A. agrarius, obtained from GenBank. We first found that the two insular populations are two clades, and that each of them is divergent from continental Eurasian populations, clustered into another clade. Each of the two insular clades appeared to be isolated in spite of land connection to nearby continent during the last glacial period, and we considered the two insular forms as A. a. insulaemus and A. a. chejuensis and one continental Eurasian form as A. a. agrarius, although further analyses are needed to confirm our present findings. Additionally, the Taiwan clade seemed to be composed of two subclades (western and eastern), separated by Taiwan’s central mountain range

Drastic population fluctuations explain the rapid extinction of the passenger pigeon

To assess the role of human disturbances in species' extinction requires an understanding of the species population history before human impact. The passenger pigeon was once the most abundant bird in the world, with a population size estimated at 3-5 billion in the 1800s; its abrupt extinction in 1914 raises the question of how such an abundant bird could have been driven to extinction in mere decades. Although human exploitation is often blamed, the role of natural population dynamics in the passenger pigeon's extinction remains unexplored. Applying high-throughput sequencing technologies to obtain sequences from most of the genome, we calculated that the passenger pigeon's effective population size throughout the last million years was persistently about 1/10,000 of the 1800's estimated number of individuals, a ratio 1,000-times lower than typically found. This result suggests that the passenger pigeon was not always super abundant but experienced dramatic population fluctuations, resembling those of an "outbreak" species. Ecological niche models supported inference of drastic changes in the extent of its breeding range over the last glacial-interglacial cycle. An estimate of acorn-based carrying capacity during the past 21,000 y showed great year-to-year variations. Based on our results, we hypothesize that ecological conditions that dramatically reduced population size under natural conditions could have interacted with human exploitation in causing the passenger pigeon's rapid demise. Our study illustrates that even species as abundant as the passenger pigeon can be vulnerable to human threats if they are subject to dramatic population fluctuations, and provides a new perspective on the greatest human-caused extinction in recorded history

Genomic Analysis of Demographic History and Ecological Niche Modeling in the Endangered Sumatran Rhinoceros Dicerorhinus sumatrensis

The vertebrate extinction rate over the past century is approximately 22–100 times greater than background extinction rates [1], and large mammals are particularly at risk [2, 3]. Quaternary megafaunal extinctions have been attributed to climate change [4], overexploitation [5], or a combination of the two [6]. Rhinoceroses (Family: Rhinocerotidae) have a rich fossil history replete with iconic examples of climate-induced extinctions [7], but current pressures threaten to eliminate this group entirely. The Sumatran rhinoceros(Dicerorhinus sumatrensis) is among the most imperiled mammals on earth. The 2011 population was estimated at ≤216 wild individuals [8], and currently the species is extirpated, or nearly so, throughout the majority of its former range [8–12]. Understanding demographic history is important in placing current population status into a broader ecological and evolutionary context. Analysis of the Sumatran rhinoceros genome reveals extreme changes in effective population size throughout the Pleistocene. Population expansion during the early to middle Pleistocene was followed by decline. Ecological niche modeling indicated that changing climate most likely played a role in the decline of the Sumatran rhinoceros, as less suitable habitat on an emergent Sundaland corridor isolated Sumatran rhinoceros populations. By the end of the Pleistocene, the Sundaland corridor was submerged, and populations were fragmented and consequently reduced to low Holocene levels from which they would never recover. Past events denuded the Sumatran rhinoceros of genetic diversity through population decline, fragmentation, or some combination of the two and most likely made the species even more susceptible to later exploitation and habitat loss

When males live longer: Resource-driven territorial behavior drives sex-specific survival in snakes.

Phylogenetic analysis has shown that males' propensity to engage in aggressive encounters is associated with females having greater longevity. Here, we confirm the causal link between aggression and reduced longevity by looking at an egg-eating snake (Oligodon formosanus) in which females defend territories in the presence of sea turtle eggs. We monitored aggressiveness and survival at two sites: a control site with a stable supply of turtle eggs, and a second site where we collected data before and after a storm that eroded the beach on which turtles nested, thus leading to a loss of territoriality. We show that territoriality was the driver behind higher injury rates in females. Territorial females also had lower survival and decreased longevity compared with the nonterritorial males, but these differences disappeared when females were not territorial. Our study demonstrates how resource availability can influence the evolution of sex-specific patterns of survival across vertebrates

Trophic Shifts of a Generalist Consumer in Response to Resource Pulses

Trophic shifts of generalist consumers can have broad food-web and biodiversity consequences through altered trophic flows and vertical diversity. Previous studies have used trophic shifts as indicators of food-web responses to perturbations, such as species invasion, and spatial or temporal subsidies. Resource pulses, as a form of temporal subsidies, have been found to be quite common among various ecosystems, affecting organisms at multiple trophic levels. Although diet switching of generalist consumers in response to resource pulses is well documented, few studies have examined if the switch involves trophic shifts, and if so, the directions and magnitudes of the shifts. In this study, we used stable carbon and nitrogen isotopes with a Bayesian multi-source mixing model to estimate proportional contributions of three trophic groups (i.e. producer, consumer, and fungus-detritivore) to the diets of the White-footed mouse (Peromyscus leucopus) receiving an artificial seed pulse or a naturally-occurring cicadas pulse. Our results demonstrated that resource pulses can drive trophic shifts in the mice. Specifically, the producer contribution to the mouse diets was increased by 32% with the seed pulse at both sites examined. The consumer contribution to the mouse diets was also increased by 29% with the cicadas pulse in one of the two grids examined. However, the pattern was reversed in the second grid, with a 13% decrease in the consumer contribution with the cicadas pulse. These findings suggest that generalist consumers may play different functional roles in food webs under perturbations of resource pulses. This study provides one of the few highly quantitative descriptions on dietary and trophic shifts of a key consumer in forest food webs, which may help future studies to form specific predictions on changes in trophic interactions following resource pulses

Niche–trait relationships at individual and population level in three co‐occurring passerine species

Abstract The niche variation hypothesis (NVH) predicts that populations with wider niches exhibit greater morphological variation through increased interindividual differences in both niche and morphology. In this study, we examined niche–trait relationships in three passerine species (Cyanoderma ruficeps, Sinosuthora webbiana, and Zosterops simplex). A total of 289 C. ruficeps from 7 sites, 259 S. webbiana from 8 sites, and 144 Z. simplex from 6 sites were sampled along an elevation gradient (0–2,700 m) in Taiwan from 2009 to 2017. We measured bill traits (length, width, and depth of bill) and body size traits (length of head, tarsus, and wing) of the birds, which were reduced to four principal components (bill PC1, bill PC2, body size PC1, and body size PC2). We collected feather tissues for stable carbon and nitrogen isotope analyses to quantify their isotope niche. We quantified interindividual differences in isotope space and trait space with four diversity metrics (divergence, dispersion, evenness, and uniqueness) and tested whether interindividual differences in isotope space and trait space are positively associated. We quantified population isotope niche width by Bayesian ellipse area and population morphological variation by variances of the PCs. The results showed that individual uniqueness in isotope niche and bill morphology (average closeness of individuals within the population isotope/trait space) were positively associated across three species. Furthermore, isotope niche width and bill PC1 (reflecting the size of bill) variation at population level were also positively associated across the three species, supporting the NVH. Of the three species, C. ruficeps and S. webbiana showed stronger support for the NVH than Z. simplex, possibly due to the latter having narrower elevational distribution and a more specialized, plant‐based diet. The diversity metrics represented different aspects of interindividual differences in niche/trait space, and for the passerines, individual uniqueness appeared to play an important role in their niche–trait dynamics

Farmers’ Knowledge, Attitudes, and Control Practices of Rodents in an Agricultural Area of Taiwan

Rodents threaten agricultural industries and food security on a global scale. Rodent management practices routinely involve the use of chemical products, mainly anticoagulant rodenticides (ARs). An understanding of farmer rodent control behaviors is crucial in order to implement management changes to more environmentally friendly practices. In this study, we surveyed farmers in an agricultural area of northwestern Taiwan on their knowledge, attitudes, and control practices for rodent pests. From our survey sample of 126 farmers, rodents were perceived to be the most problematic for vegetable crops, followed by rice, and then fruit. Farmers in the oldest age group and those that perceived rodents to cause extensive damage to their crops were found to have the most negative attitudes toward the pests. One-third of the farmers in our survey stated they currently use rodenticides, with crop type, perceived problems caused by rodents, and attitudes toward rodents found to be important explanatory variables. Our results indicate that the use of rodenticides is reactive; farmers are more likely to apply the chemical products if they perceive rodents to cause damage. Additionally, cost–benefit assessments are likely important in governing rodent control behaviors; farmers may be more inclined to use control products that are subsidized by the government, which include ARs, when they observe damage to their crops inflicted by rodents. We also describe how ecologically based rodent management (EBRM) practices could be feasible and sustainable alternatives to rodenticide use

Farmers’ Knowledge, Attitudes, and Control Practices of Rodents in an Agricultural Area of Taiwan

Rodents threaten agricultural industries and food security on a global scale. Rodent management practices routinely involve the use of chemical products, mainly anticoagulant rodenticides (ARs). An understanding of farmer rodent control behaviors is crucial in order to implement management changes to more environmentally friendly practices. In this study, we surveyed farmers in an agricultural area of northwestern Taiwan on their knowledge, attitudes, and control practices for rodent pests. From our survey sample of 126 farmers, rodents were perceived to be the most problematic for vegetable crops, followed by rice, and then fruit. Farmers in the oldest age group and those that perceived rodents to cause extensive damage to their crops were found to have the most negative attitudes toward the pests. One-third of the farmers in our survey stated they currently use rodenticides, with crop type, perceived problems caused by rodents, and attitudes toward rodents found to be important explanatory variables. Our results indicate that the use of rodenticides is reactive; farmers are more likely to apply the chemical products if they perceive rodents to cause damage. Additionally, cost–benefit assessments are likely important in governing rodent control behaviors; farmers may be more inclined to use control products that are subsidized by the government, which include ARs, when they observe damage to their crops inflicted by rodents. We also describe how ecologically based rodent management (EBRM) practices could be feasible and sustainable alternatives to rodenticide use

Appendix A. A table listing the C and N stable-isotope composition of the plants at the study sites.

A table listing the C and N stable-isotope composition of the plants at the study sites