Thijs Janzen | bioRxiv Science

bioRxiv2016

Haplotype block dynamics in hybrid populations

When species originate through hybridization, the genomes of the ancestral species are blended together. Over time genomic blocks that originate from either one of the ancestral species accumulate in the hybrid genome through genetic recombination. Modeling the accumulation of ancestry blocks can elucidate processes and patterns of genomic admixture. However, previous models have ignored ancestry block dynamics for chromosomes that consist of a discrete, finite number of chromosomal elements. Here we present an analytical treatment of the dynamics of the mean number of blocks over time, for continuous and discrete chromosomes, in finite and infinite populations. We describe the mean number of haplotype blocks as a universal function dependent on population size, the number of genomic elements per chromosome, the number of recombination events, and the initial relative frequency of the ancestral species.

Evolutionary Biology↗

bioRxiv2016

Stochastic processes dominate community assembly in cichlid communities in Lake Tanganyika

The African Great Lakes are characterized by an extraordinary diversity of endemic cichlid fish species. The cause of this diversity is still largely unknown. Most studies have tried to solve this question by focusing on macro-evolutionary processes, such as speciation. However, the ecological processes determining local cichlid diversity have so far been understudied, even though knowledge on these might be crucial for understanding larger scale biodiversity patterns.\n\nUsing trait, environmental and abundance data of cichlid fishes along 36 transects, we have studied how differences in local environmental conditions influence cichlid community assembly in the littoral of Lake Tanganyika, Zambia. We investigated changes in average trait values and in trait-based community assembly processes along three key environmental gradients.\n\nSpecies diversity and local abundance decreased with increasing sand cover and diet-associated traits changed with depth. Analyses on within-community trait diversity patterns indicated that cichlid community assembly was mainly driven by stochastic processes, to a smaller extent by processes that limit the similarity among co-existing species and least by filtering processes that limit the range of species traits occurring in an environment. Despite, the low impact of habitat filtering processes, we find community dissimilarity to increase with increasing environmental difference.\n\nOur results suggest that local environmental conditions determine cichlid abundance, while the predominance of stochastic community assembly across all environments explains why the communities with the highest abundances contain most species.

Ecology↗