Species-specific and habitat correlates of butterfly dispersal using ability: Exploring dispersal using patterns of population genetic structure

Abstract

Dispersal ability of a species is a key ecological characteristic, influencing processes such as adaptation, community dynamics, genetic structure, distribution, and range size. It is determined by both intrinsic species traits and extrinsic landscape-related properties. Using butterflies as a model system, the following questions were addressed: a) Given similar extrinsic factors, which intrinsic species trait(s) explain dispersal ability b) Can one of these traits be used as a proxy for dispersal ability c) What is the effect of interactions between traits and phylogenetic relatedness on dispersal ability

Four datasets, using different measures of dispersal, were compiled from published literature. The first dataset used mean dispersal distances from capture-mark-recapture studies, while the other three used mobility indices. Data for six traits potentially affecting dispersal ability were collected: wingspan, larval host plant specificity, adult habitat specificity, mate location strategy, voltinism, and flight period duration. Each dataset was subjected to both unifactorial and multifactorial phylogenetically controlled analyses.

Among the factors considered, wingspan was the most important determinant of dispersal ability, though the predictive power of regression models was low. Voltinism and flight period duration also influenced dispersal ability, particularly in temperate species. Interactions between traits did not affect dispersal ability, and phylogenetic relatedness was significant in one dataset. While using wingspan as the sole proxy for dispersal ability may be problematic, it is often the only easily accessible species-specific trait for many species worldwide. Thus, wingspan can serve as a satisfactory proxy when carefully interpreted, especially in large-scale comparative analyses.

Dispersal ability is central to species biology, affecting local adaptation, population and community dynamics, and genetic structure. Dispersal, or lack thereof, determines species survival in fragmented landscapes by influencing immigration and emigration rates between habitat patches. Among intrinsic factors, wingspan has recently been shown to explain substantial variance in butterfly dispersal ability. Operating on this premise, this study tested whether differences in wingspan translate into differences in population genetic structure.

A comparative approach was adopted using two closely related species with similar ecologies and traits affecting dispersal ability, except for wingspan: Melanitis leda (ML, wingspan 60-80 mm) and Ypthima baldus (YB, wingspan 30-40 mm). Both species were collected from the same areas along the Western Ghats. The hypothesis tested was: does the species with a larger wingspan (ML) exhibit a more homogeneous population genetic structure compared to the smaller-winged species (YB)

Molecular data in the form of Amplified Fragment Length Polymorphisms (AFLPs) were used, with two types of analyses performed:

Individual-based analyses to obtain overall patterns in the dataset.

Population-based analyses after assigning individuals into populations.

In all analyses, YB (smaller wingspan) exhibited greater genetic structure than ML (larger wingspan). This study is among the few to adopt a robust comparative approach to establish a relationship between dispersal-related traits and population genetic structure. AFLPs successfully detected differences in genetic structures over relatively small geographic areas, and efforts were made to quantitatively compare population genetic patterns between the two species.Dispersal ability of a species is a key ecological characteristic, influencing processes such as adaptation, community dynamics, genetic structure, distribution, and range size. It is determined by both intrinsic species traits and extrinsic landscape-related properties. Using butterflies as a model system, the following questions were addressed: a) Given similar extrinsic factors, which intrinsic species trait(s) explain dispersal ability b) Can one of these traits be used as a proxy for dispersal ability c) What is the effect of interactions between traits and phylogenetic relatedness on dispersal ability

Four datasets, using different measures of dispersal, were compiled from published literature. The first dataset used mean dispersal distances from capture-mark-recapture studies, while the other three used mobility indices. Data for six traits potentially affecting dispersal ability were collected: wingspan, larval host plant specificity, adult habitat specificity, mate location strategy, voltinism, and flight period duration. Each dataset was subjected to both unifactorial and multifactorial phylogenetically controlled analyses.

Among the factors considered, wingspan was the most important determinant of dispersal ability, though the predictive power of regression models was low. Voltinism and flight period duration also influenced dispersal ability, particularly in temperate species. Interactions between traits did not affect dispersal ability, and phylogenetic relatedness was significant in one dataset. While using wingspan as the sole proxy for dispersal ability may be problematic, it is often the only easily accessible species-specific trait for many species worldwide. Thus, wingspan can serve as a satisfactory proxy when carefully interpreted, especially in large-scale comparative analyses.

Dispersal ability is central to species biology, affecting local adaptation, population and community dynamics, and genetic structure. Dispersal, or lack thereof, determines species survival in fragmented landscapes by influencing immigration and emigration rates between habitat patches. Among intrinsic factors, wingspan has recently been shown to explain substantial variance in butterfly dispersal ability. Operating on this premise, this study tested whether differences in wingspan translate into differences in population genetic structure.

A comparative approach was adopted using two closely related species with similar ecologies and traits affecting dispersal ability, except for wingspan: Melanitis leda (ML, wingspan 60-80 mm) and Ypthima baldus (YB, wingspan 30-40 mm). Both species were collected from the same areas along the Western Ghats. The hypothesis tested was: does the species with a larger wingspan (ML) exhibit a more homogeneous population genetic structure compared to the smaller-winged species (YB)

Molecular data in the form of Amplified Fragment Length Polymorphisms (AFLPs) were used, with two types of analyses performed:

Individual-based analyses to obtain overall patterns in the dataset.

Population-based analyses after assigning individuals into populations.

In all analyses, YB (smaller wingspan) exhibited greater genetic structure than ML (larger wingspan). This study is among the few to adopt a robust comparative approach to establish a relationship between dispersal-related traits and population genetic structure. AFLPs successfully detected differences in genetic structures over relatively small geographic areas, and efforts were made to quantitatively compare population genetic patterns between the two species.