Parasite diversity, patterns of MHC II variation and olfactory based mate choice in diverging three-spined stickleback ecotypes

Abstract

Ecological speciation has been the subject of intense research in evolutionary biology but the genetic basis of the actual mechanism driving reproductive isolation has rarely been identified. The extreme polymorphism of the major histocompatibility complex (MHC), probably maintained by parasite-mediated selection, has been proposed as a potential driver of population divergence. We performed an integrative field and experimental study using three-spined stickleback river and lake ecotypes. We characterized their parasite load and variation at MHC class II loci. Fish from lakes and rivers harbor contrasting parasite communities and populations possess different MHC allele pools that could be the result of a combined action of genetic drift and parasite-mediated selection. We show that individual MHC class II diversity varies among populations and is lower in river ecotypes. Our results suggest the action of homogenizing selection within habitat type and diverging selection between habitat types. Finally, reproductive isolation was suggested by experimental evidence: in a flow channel design females preferred assortatively the odor of their sympatric male. This demonstrates the role of olfactory cues in maintaining reproductive isolation between diverging fish ecotypes

Contrasting responses to selection in class I and class IIα major histocompatibility-linked markers in salmon

“…However, there appears to be a great deal of species-to-species variation in the relative levels of MHC and neutral variability among populations. Among-population differentiation at MHC loci has been observed to range from lower than (Sommer, 2003;Aguilar et al, 2004), similar to (Boyce et al, 1997;Parker et al, 1999;Hedrick et al, 2001;Huang and Yu, 2003), to higher than that at neutral loci (Miller et al, 2001;Beacham et al, 2004), reflecting differences in the relative strengths of natural selection, genetic drift and gene flow across species (Eizaguirre et al, 2010). Indeed, the relative levels of neutral and MHC variation within and among populations can vary across closely related species (Hambuch and Lacey, 2002;Jarvi et al, 2004), and even within a species depending on the spatial scale of analysis .…”

“…Moreover, the results suggested that additive allelic effects were more important than heterozygote advantage for individual survival (de Eyto et al, 2007). Sexual selection could also favor individuals carrying specific resistance alleles against common parasites in different populations, and differences in MHC composition due to divergent parasite-mediated selection could be further maintained by assortative mating of females with locally adapted males (Eizaguirre et al, 2009(Eizaguirre et al, , 2010.…”

The contribution of post-copulatory mechanisms to incipient ecological speciation in sticklebacks

“…We can hypothesize that high sperm concentration in lake males and high sperm speed in river males might act in a compensatory manner in competitive situations, leading to balanced paternity. In addition, precopulatory reproductive isolation is relatively strong in this system, which may decrease selection for sympatric sperm precedence as a reproductive barrier [5,13].…”

Effects of forsythoside on lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages

“…Its identification is considered as a major breakthrough in the identification as a key component of the adaptive immune system to respond to pathogen infection (Christophe et al, 2011). MHC-II molecules are cell surface glycoproteins that bind self and antigenic peptides and present them to T cells to initiate an immune response (Germain et al, 1993).…”