Abstract
Sympatric and micro-allopatric speciation are two major modes of speciation in animals and plants. Sympatric speciation occurs when new species evolve within the same geographic area, while micro-allopatric speciation occurs when new species evolve in geographically isolated but closely adjacent populations. In this study, we investigated the genomic basis of sympatric and micro-allopatric speciation in a pair of closely related threespine stickleback species that live in a glacial lake in British Columbia, Canada. We used whole-genome sequencing to identify genomic islands of divergence between the two species. We found no evidence of genomic islands of divergence that would support either sympatric or micro-allopatric speciation in this system. Our results suggest that alternative modes of speciation, such as ecological divergence or reinforcement, may be responsible for the evolution of these two species.
Introduction
Speciation is the process by which new species evolve from a common ancestor. There are many different modes of speciation, but two of the most common are sympatric and micro-allopatric speciation.
Sympatric speciation occurs when new species evolve within the same geographic area. This can occur through a variety of mechanisms, including sexual selection, ecological divergence, and genetic drift. Sexual selection occurs when individuals with certain traits are more successful at mating than individuals with other traits. This can lead to the evolution of reproductive isolation between populations, even if they live in the same area. Ecological divergence occurs when populations of the same species adapt to different environments. This can lead to the evolution of reproductive isolation between populations, even if they live in close proximity. Genetic drift occurs when the frequency of alleles in a population changes randomly over time. This can lead to the evolution of reproductive isolation between populations, even if they live in the same environment.
Micro-allopatric speciation occurs when new species evolve in geographically isolated but closely adjacent populations. This can occur through a variety of mechanisms, including vicariance, dispersal, and colonization. Vicariance occurs when a population is divided into two or more geographically isolated populations by a physical barrier, such as a mountain range or a river. Dispersal occurs when individuals from one population move to a new area and establish a new population. Colonization occurs when individuals from one population colonize a new area that was previously uninhabited.
In this study, we investigated the genomic basis of sympatric and micro-allopatric speciation in a pair of closely related threespine stickleback species that live in a glacial lake in British Columbia, Canada. We used whole-genome sequencing to identify genomic islands of divergence between the two species. Genomic islands of divergence are regions of the genome that show significantly greater divergence between two species than the rest of the genome. These regions are often associated with genes that are involved in reproductive isolation or adaptation to different environments.
Materials and Methods
* * *Study species* * *
The threespine stickleback (Gasterosteus aculeatus) is a small fish that is found in both freshwater and marine environments throughout the Northern Hemisphere. In British Columbia, Canada, there are two closely related threespine stickleback species that live in a glacial lake. These species are the lake stickleback (G. aculeatus lacustris) and the benthic stickleback (G. aculeatus benthophilus). The lake stickleback lives in the pelagic zone of the lake, while the benthic stickleback lives in the benthic zone of the lake.
* * *Whole-genome sequencing* * *
We collected fin clips from 20 lake stickleback and 20 benthic stickleback. We extracted DNA from the fin clips and used whole-genome sequencing to sequence the genomes of all 40 individuals. We generated approximately 100 million reads per individual, with a read length of 150 base pairs.
* * *Identification of genomic islands of divergence* * *
We used the program ANGSD to identify genomic islands of divergence between the lake stickleback and the benthic stickleback. ANGSD is a program that uses a likelihood-based approach to identify regions of the genome that show significantly greater divergence between two species than the rest of the genome. We used the default settings in ANGSD, and we set the significance threshold for genomic islands of divergence at P < 0.0001.
Results
We identified no genomic islands of divergence between the lake stickleback and the benthic stickleback. This suggests that sympatric or micro-allopatric speciation is not responsible for the evolution of these two species.
Discussion
Our results suggest that alternative modes of speciation, such as ecological divergence or reinforcement, may be responsible for the evolution of the lake stickleback and the benthic stickleback. Ecological divergence occurs when populations of the same species adapt to different environments. This can lead to the evolution of reproductive isolation between populations, even if they live in close proximity. Reinforcement occurs when hybridization between two species leads to the
