Intertidal Microhabitat and Selection at MPI: Interlocus Contrasts in the Northern Acorn Barnacle, Semibalanus balanoides

Abstract

Barnacles were sampled from various microhabitats in the rocky intertidal at multiple sites in two years. At sites in which there were large differences among microhabitats in temperature profiles, Mpi genotype frequencies were consistently and significantly different. Genotype frequencies for another allozyme locus (Gpi) as well as a DNA marker shown to be neutral (the mtDNA control region) were statistically homogeneous among thermal microhabitats at all sites in both years. The data indicate that temperature and/or desiccation mediated selection is operating at Mpi or a linked locus and that Mpi genotypes experience differential mortality in the various habitat types. If the relative fitness of genotypes is dependent on habitat type, the Mpi polymorphism may be actively maintained by a Levene model of balancing selection (Levene 1953). Because barnacle larvae are produced in abundance each year and spend five to eight weeks dispersing in the water column, there is little opportunity for the accumulation of adaptive divergence over the environmental grain size relevant in intertidal habitats. The Mpi polymorphism may be an important component of a suite of traits involved in the adaptation of barnacles to heterogeneous environments. Due to the relatively high concentration of mannose in a variety of algal groups, the metabolism of mannose may substantially affect individual performance and fitness in this and other species that feed on algae and phytoplankton. Because the Mpi locus is one of the most strongly polymorphic in marine organisms, these findings may be relevant for a diversity of other such species.

Genetic and epigenetic variation in Spartina alterniflora following the Deepwater Horizon oil spill

“…Populations in coastal habitats, and salt marshes in particular, have long been models for phenotypic differentiation across natural environmental gradients (Schmidt & Rand, 1999; Schmidt et al., 2008), and we expected to detect population‐level differentiation of DNA methylation in response to oil contamination as well (Foust et al., 2016; Richards et al., 2012). The idea that epigenetic mechanisms can contribute to population differentiation as a source of heritable phenotypic variation has been challenged in recent literature (Laland et al., 2014; Wibowo et al., 2016).…”

“…Classic population genetics studies demonstrate that natural selection in different microhabitats can result in associations of genotypes, or alleles of candidate genes, with habitat type (e.g., Hamrick & Allard, 1972; Salzman, 1985; Schmidt & Rand, 1999; Schmidt et al., 2008). In concert with other evolutionary mechanisms, disturbance events may also create population genetic structure, by diminishing standing genetic diversity through mortality (Hermisson & Pennings, 2005; Orr & Betancourt, 2001).…”

Islands Increase Genetic Subdivision and Disrupt Patterns of Connectivity of Intertidal Snails in a Complex Archipelago

“…Although we found a moderate overall deficit of heterozygotes, this was not associated with linkage disequilibrium, so there is no evidence that our samples of A. constricta include multiple species. Another possible cause of subdivision is local selection, which has been found at some allozyme loci in other intertidal species (e.g., Johnson 1971;Hilbish and Koehn 1985;Johannesson and Tatarenkov 1997;Schmidt and Rand 1999). We characterized physical and biological aspects of our study sites from throughout the Abrolhos Islands, and multivariate de-scriptors predict distributions of intertidal gastropods (Johnson and Black 1997) and variation in size and shape of shells in B. vittatum (Johnson and Black 2000).…”

Mitochondrial DNA variation in the caramote prawn Penaeus (Melicertus) kerathurus across a transition zone in the Mediterranean Sea

“…The large climatic fluctuations during the Quaternary have led to the assumption that vicariance is the most likely model of speciation promoting genetic discontinuities across geographical ranges (McMillan and Palumbi 1995;Cunningham and Collins 1998;Benzie 2000). However, other contemporary factors that limit effective genetic dispersal, including oceanographic currents, isolation-bydistance, habitat discontinuities, larval behaviour and local adaptation (Johnson and Black 1995;Benzi and Williams 1997;Palumbi et al 1997;Schmidt and Rand 1999;Riginos and Nachman 2001), may also play a pivotal role. These factors may be important singly or in combination, and their relative contributions are hard to disentangle.…”