Genetic pool information reflects highly suitable areas: the case of two parapatric endangered species of Tuco-tucos (Rodentia: Ctenomiydae)

Influences of landscape characteristics and historical barriers on the population genetic structure in the endangered sand-dune subterranean rodent Ctenomys australis

Understanding the processes and patterns of local adaptation and migration involves an exhaustive knowledge of how landscape features and population distances shape the genetic variation at the geographical level. Ctenomys australis is an endangered subterranean rodent characterized by having a restricted geographic range immerse in a highly fragmented sand dune landscape in the Southeast of Buenos Aires province, Argentina. We use 13 microsatellite loci in a total of 194 individuals from 13 sampling sites to assess the dispersal patterns and population structure in the complete geographic range of this endemic species. Our analyses show that populations are highly structured with low rates of gene flow among them. Genetic differentiation among sampling sites was consistent with an isolation by distance pattern, however, an important fraction of the population differentiation was explained by natural barriers such as rivers and streams. Although the individuals were sampled at locations distanced from each other, we also use some landscape genetics approaches to evaluate the effects of landscape configuration on the genetic connectivity among populations. These analyses showed that the sand dune habitat availability (the most suitable habitat for the occupation of the species), was one of the main factors that explained the differentiation patterns of the different sampling sites located on both sides of the Quequén Salado River. Finally, habitat availability was directly associated with the width of the sand dune landscape in the Southeast of Buenos Aires province, finding the greatest genetic differentiation among the populations of the Northeast, where this landscape is narrower.

Genetic Analysis of Populations of the Peach Fruit Fly, Bactrocera zonata (Diptera: Tephritidae), in Iran

Bactrocera zonata (Saunders) as one of the most devastating species of the genus Bactrocera is a notorious polyphagous fruit fly pest attacking lots of commercially important host plant species in many parts of the world including Iran. Despite economic importance, the population genetics of B. zonata have remained relatively unexplored in the country. In this study, the genetic structure, genetic diversity, and demographic history of this pest in Iran were investigated on the basis of cytochrome oxidase c subunit 1 (COI) sequences. A total of 21 haplotypes were identified from 66 individuals collected from seven locations. Genetic diversity indices (number of haplotypes, haplotype diversity, and nucleotide diversity) revealed high genetic diversity without any isolation by distance among the geographic areas. An overall low level of genetic differentiation between populations revealed by genetic structure analysis reinforces the hypothesis of free movement of flies throughout the geographic areas. Non-significant correlation between genetic distances and geographic distances was an indication of a high level of gene flow among the studied populations of the pest. In addition, the recent population expansion following a recent past bottleneck could be a factor that might be contributed to the overall low level of the genetic structure. Mismatch distribution analysis as well as Tajima's D and Fu's F_S tests strengthens the likelihood of a recent expanded population following a population bottleneck.

Can Niche Modeling and Geometric Morphometrics Document Competitive Exclusion in a Pair of Subterranean Rodents (Genus Ctenomys) with Tiny Parapatric Distributions?

Species with similar ecological requirements coexisting in the same geographic region are prone to competitively exclude each other. Alternatively, they may coexist if character displacement acts to change the niche requirements of one or both species. We used two methodological approaches (ecological niche modeling [ENM] and geometric morphometrics) to test two hypotheses: given their behavioral, morphological, and ecological similarities, one species competitively excludes the other; and, character displacement enables their coexistence at two sites in which the species are known to occur in sympatry. The results from the ENM-based approach did not provide evidence for competitive exclusion; however, the morphometric analyses documented displacement in size of C. minutus. This result, suggests that C. minutus might exclude C. flamarioni from areas with softer soils and higher food availability. We stress the importance of using multiple methodological approaches when testing prediction of competitive exclusion. However, both methods had limited explanatory power given that the focal species possess truly peculiar distributions, being largely parapatric and restricted to narrow, small geographic areas with a strange distribution and there is a need to search for additional methods. We discuss the idiosyncrasy of the ENM-based approach when applied to organisms with subterranean habits.

Wet soils affect habitat selection of a solitary subterranean rodent (Ctenomys minutus) in a Neotropical region

Subterranean rodents are characterized by limited individual mobility and patchy distribution of local populations. Habitat patches where the species is absent may either be unoccupied, but suitable patches, or in fact unsuitable as habitat due to specific habitat features. In the coastal plain of southern Brazil, Ctenomys minutus (Ctenomyidae) inhabits sandy grasslands and dunes. The aim of our study was to analyze the relationship between the distribution of this subterranean rodent and its environment. We considered vegetation and soil features. Our results showed that habitat occupancy patterns of C. minutus are determined by soil moisture and vegetation (food supply), but there might be other habitat features that regulate the habitat choice of this mammal. Habitat discontinuities in the coastal plain of southern Brazil, with numerous barriers to dispersal, are responsible for restricting individuals to their natal areas. This might result in increased intraspecific competition within each population and, consequently, in inbreeding.

Os roedores subterrâneos são caracterizados pela baixa mobilidade dos indivíduos e por apresentarem populações distribuídas em manchas de habitat. As manchas em que os indivíduos estão ausentes podem ser locais desocupados, porém que apresentam condições adequadas para a ocupação, ou de fato serem locais inadequados devido a algumas características ambientais específicas. Na planície costeira do sul do Brasil, a espécie Ctenomys minutus (Ctenomyidae) habita regiões de campos arenosos e dunas costeiras. O objetivo do presente estudo foi analisar a relação entre a distribuição deste roedor subterrâneo e o ambiente em que ele habita. Para tal, consideramos características da vegetação e do solo. Nossos resultados demonstraram que o padrão de ocupação de C. minutus é determinado pela umidade do solo e vegetação (recurso alimentar), mas podem existir outras características que regulam a escolha do habitat deste mamífero. As descontinuidades de habitat na planície costeira do sul do Brasil, com inúmeras barreiras para a dispersão da espécie, são responsáveis por restringir os indivíduos as suas áreas natais. Isso pode resultar no aumento da competição intra-específica dentro das populações e, consequentemente, na endogamia.

Niche suitability affects development: skull asymmetry increases in less suitable areas

For conservation purposes, it is important to take into account the suitability of a species to particular habitats; this information may predict the long-term survival of a species. In this sense, morphological measures of developmental stress, such as fluctuating asymmetry, can be proxies for an individual’s performance in different regions. In this study, we conducted tests to determine whether areas with different levels of suitability for a species (generated by ecological niche models) were congruent with morphological markers that reflect environmental stress and morphological variance. We generated a Maxent niche model and compared the suitability assessments of several areas with the skull morphology data (fluctuating asymmetry and morphological disparity) of populations of the Atlantic forest endemic to Brazil rodent Akodon cursor. Our analyses showed a significant negative relationship between suitability levels and fluctuating asymmetry levels, which indicates that in less suitable areas, the individuals experience numerous disturbances during skull ontogeny. We have not found an association between morphological variance and environmental suitability. As expected, these results suggest that in environments with a lower suitability, developmental stress is increased. Such information is helpful in the understanding of the species evolution and in the selection of priority areas for the conservation of species.

Sharing the space: distribution, habitat segregation and delimitation of a new sympatric area of subterranean rodents

Subterranean rodents of the genus Ctenomys usually present an allopatric or parapatric distribution. Currently, two cases of sympatry have been recognized for the genus in the coastal dunes of southern Argentina and southern Brazil. In this context, they are ideal models to test hypotheses about the factors that delimit the patterns of space use and to understand interspecific interactions in small mammals. We investigated the vegetation structure, plant biomass and soil hardness selected by two species of subterranean rodents (Ctenomys flamarioni and C. minutus) when distributed in sympatry and allopatry from nine different areas along the line of coastal dunes in southern Brazil. In addition, our work presents a new record of a third area of sympatry for the genus Ctenomys. Ctenomys flamarioni and C. minutus show habitat segregation in the area where they occur in sympatry. These species show segregation in their selection of microhabitats, differing in relation to soil hardness, plant biomass, and plant cover. Ctenomys flamarioni showed a distinction in habitat selection when occurring in allopatry and sympatry, whereas C. minutus selected the same habitat characteristics under both conditions. A possible explanation to the observed pattern is that these species have acquired different adaptations over time which allows them the ability to exploit different resources and thus avoid competitive interactions all together.