Biology subjects

Salazar, C.

Publications and source records attributed to Salazar, C..

4 recordsLinked to original sources

bioRxiv2018

Recombination rate variation shapes barriers to introgression across butterfly genomes

Hybridisation and introgression can dramatically alter the relationships among groups of species, leading to phylogenetic discordance across the genome and between populations. Introgression can also erode species differences over time, but selection against introgression at certain loci acts to maintain post-mating species barriers. Theory predicts that species barriers made up of many loci throughout the genome should lead to a broad correlation between introgression and recombination rate, which determines the extent to which selection on deleterious foreign alleles will affect neutral alleles at physically linked loci. Here we describe the variation in genealogical relationships across the genome among three species of Heliconius butterflies: H. melpomene, H. cydno and H. timareta, using whole genomes of 92 individuals, and ask whether this variation can be explained by heterogeneous barriers to introgression. We find that species relationships vary predictably at the chromosomal scale. By quantifying recombination rate and admixture proportions, we then show that rates of introgression are predicted by variation in recombination rate. This implies that species barriers are highly polygenic, with selection acting against introgressed alleles across most of the genome. In addition, long chromosomes, which have lower recombination rates, produce stronger barriers on average than short chromosomes. Finally, we find a consistent difference between two species pairs on either side of the Andes, which suggests differences in the architecture of the species barriers. Our findings illustrate how the combined effects of hybridisation, recombination and natural selection, acting at multitudes of loci over long periods, can dramatically sculpt the phylogenetic relationships among species.

evolutionary biology↗

bioRxiv2018

Gene flow and Andean uplift shape the diversification of Gasteracantha cancriformis (Araneae: Araneidae) in Northern South America

AimThe Andean uplift has played a major role shaping the current Neotropical biodiversity. However, in arthropods other than butterflies, little is known about how this geographic barrier has impacted species historical diversification. Here we examined the phylogeography of the widespread and color polymorphic spider Gasteracantha cancriformis to: (i) evaluate the effect of the northern Andean uplift on its divergence and, (ii) assess whether its diversification occurred in the presence of gene flow.\n\nLocationNorthern Andes and Brazil\n\nMethodsWe inferred phylogenetic relationships and divergence times in G. cancriformis using mitochondrial and nuclear data from 105 individuals in northern South America. Genetic diversity, divergence and population structure were quantified. We also compared multiple demographic scenarios for this species using a model-based approach (PHRAPL) to establish divergence with or without gene flow. Finally, we evaluated the association between genetic variation and color polymorphism.\n\nResultsBoth nuclear and mitochondrial data supported two well-differentiated clades, which correspond to populations occurring in opposite sides of the Eastern cordillera of the Colombian Andes. The splitting between these clades occurred in the early Pleistocene, around 2.13 million years ago (95% HPD = 0.98-3.93).\n\nDespite this vicariant event, there is shared genetic variation between the clades, which is better explained by a scenario of historical divergence in the face of gene flow. Color polymorphism was randomly scattered in both clades and is not statistically associated with the genetic variation studied here.\n\nMain ConclusionsThe final uplift of Eastern cordillera of the Colombian Andes was identified as the major force that shaped the diversification of G. cancriformis in Northern South America, resulting in a cis- and trans-Andean phylogeographic structure for the species. The divergence in the face of gene flow between cis- and trans-Andean populations found for this spider has been likely facilitated by the presence of low-elevation passes across the Eastern Colombian cordillera. Our work constitutes the first example where the Andean uplift coupled with gene flow influenced the evolutionary history of an arachnid lineage.

evolutionary biology↗

bioRxiv2017

Patterns of Z chromosome divergence among Heliconius species highlight the importance of historical demography

Sex chromosomes are disproportionately involved in reproductive isolation and adaptation. In support of such a large-X effect, genome scans between recently diverged populations or species pairs often identify distinct patterns of divergence on the sex chromosome compared to autosomes. When measures of divergence between populations are higher on the sex chromosome compared to autosomes, such patterns could be interpreted as evidence for faster divergence on the sex chromosome, i.e. faster-X, or barriers to gene flow on the sex chromosome. However, demographic changes can strongly skew divergence estimates and are not always taken into consideration. We used 224 whole genome sequences representing 36 populations from two Heliconius butterfly clades (H. erato and H. melpomene) to explore patterns of Z chromosome divergence. We show that increased divergence compared to equilibrium expectations can in many cases be explained by demographic change. Among Heliconius erato populations, for instance, population size increase in the ancestral population can explain increased absolute divergence measures on the Z chromosome compared to the autosomes, as a result of increased ancestral Z chromosome genetic diversity. Nonetheless, we do identify increased divergence on the Z chromosome relative to the autosomes in parapatric or sympatric species comparisons that imply post-zygotic reproductive barriers. Using simulations, we show that this is consistent with reduced gene flow on the Z chromosome, perhaps due to greater accumulation of species incompatibilities. Our work demonstrates the importance of constructing an appropriate demographic null model in order to interpret patterns of divergence on the Z chromosome, but nonetheless provides evidence to support the Z chromosome as a strong barrier to gene flow in incipient Heliconius butterfly species.

evolutionary biology↗

bioRxiv2017

What shapes the continuum of reproductive isolation? Lessons from Heliconius butterflies.

The process by which species evolve can be illuminated by investigating barriers that limit gene flow between taxa. Recent radiations, such as Heliconius butterflies, offer the opportunity to compare isolation between pairs of taxa at different stages of ecological, geographic and phylogenetic divergence. We carry out a comparative analysis of existing and novel data in order to quantify the strength and direction of isolating barriers within a well-studied clade of Heliconius. Our results highlight that increased divergence is associated with the accumulation of stronger and more numerous barriers to gene flow. Wing pattern is both under natural selection for Mullerian mimicry and involved in mate choice, and therefore underlies several isolating barriers. However, pairs which share a similar wing pattern, also display strong reproductive isolation mediated by traits other than wing pattern. This suggests that, while wing pattern is a key factor for early stages of divergence, it is not essential at a higher level. Additional factors including habitat isolation, hybrid sterility and chemically-mediated mate choice are associated with complete speciation. Therefore, although most previous work has emphasised the role of wing pattern, our comparative results highlight that speciation is a multidimensional process, whose completion is stabilized by many factors.

evolutionary biology↗