Assessing species boundaries using multilocus species delimitation in a morphologically conserved group of neotropical freshwater fishes, the Poecilia sphenops species complex (Poeciliidae).

Accurately delimiting species is fundamentally important for understanding species diversity and distributions and devising effective strategies to conserve biodiversity. However, species delimitation is problematic in many taxa, including 'non-adaptive radiations' containing morphologically cryptic lineages. Fortunately, coalescent-based species delimitation methods hold promise for objectively estimating species limits in such radiations, using multilocus genetic data. Using coalescent-based approaches, we delimit species and infer evolutionary relationships in a morphologically conserved group of Central American freshwater fishes, the Poecilia sphenops species complex. Phylogenetic analyses of multiple genetic markers (sequences of two mitochondrial DNA genes and five nuclear loci) from 10/15 species and genetic lineages recognized in the group support the P. sphenops species complex as monophyletic with respect to outgroups, with eight mitochondrial 'major-lineages' diverged by ≥2% pairwise genetic distances. From general mixed Yule-coalescent models, we discovered (conservatively) 10 species within our concatenated mitochondrial DNA dataset, 9 of which were strongly supported by subsequent multilocus Bayesian species delimitation and species tree analyses. Results suggested species-level diversity is underestimated or overestimated by at least ~15% in different lineages in the complex. Nonparametric statistics and coalescent simulations indicate genealogical discordance among our gene tree results has mainly derived from interspecific hybridization in the nuclear genome. However, mitochondrial DNA show little evidence for introgression, and our species delimitation results appear robust to effects of this process. Overall, our findings support the utility of combining multiple lines of genetic evidence and broad phylogeographical sampling to discover and validate species using coalescent-based methods. Our study also highlights the importance of testing for hybridization versus incomplete lineage sorting, which aids inference of not only species limits but also evolutionary processes influencing genetic diversity.

NATURAL SELECTION RESULTING FROM FEMALE BREEDING COMPETITION IN A PACIFIC SALMON (COHO: ONCORHYNCHUS KISUTCH).

We studied breeding competition among wild female coho salmon (Oncorhynchus kisutch) and quantified natural selection acting on two important female characters: body size and kype size (a secondary sexual character used for fighting). We found that body size contributed to adult female fitness in three ways, through 1) an increased initial biomass of egg production, 2) the ability to acquire a high-quality territory for egg development, and 3) success in nest defense. These factors together resulted in as much as a 23-fold fitness advantage to the largest females in the population. The initial investment into egg production accounted for 50-60% of the measured intensity of natural selection on female body size. The effective investment into egg production (after female competition for territories) accounted for 40-50% of natural selection on female body size. Therefore, success in breeding competition is about as important as egg production in the current evolution of female body size. This is contrary to the expectation based on most fisheries literature. The size of a female's kype was also important to female reproductive success, although its contribution could not be separated from that of body size in our study. The strong natural selection that we have found for female competitive ability is presumably the basis for the evolution of female parental care in salmonids.