Are we underestimating the occurrence of sympatric populations?

Abstract

Sympatric populations are conspecific populations that coexist spatially. They are of interest in evolutionary biology by representing the potential first steps of sympatric speciation and are important to identify and monitor in conservation management. Reviewing the literature pertaining to sympatric populations, we find that most cases of sympatry appear coupled to phenotypic divergence, implying ease of detection. In comparison, phenotypically cryptic, sympatric populations seem rarely documented. We explore the statistical power for detecting population mixtures from genetic marker data, using commonly applied tests for heterozygote deficiency (i.e., Wahlund effect) and the structure software, through computer simulations. We find that both tests are efficient at detecting population mixture only when genetic differentiation is high, sample size and number of genetic markers are reasonable and the sympatric populations happen to occur in similar proportions in the sample. We present an approximate expression based on these experimental factors for the lower limit of F , beyond which power for structure collapses and only the heterozygote-deficiency tests retain some, although low, power. The findings suggest that cases of cryptic sympatry may have passed unnoticed in population genetic screenings using number of loci typical of the pre-genomics era. Hence, cryptic sympatric populations may be more common than hitherto thought, and we urge more attention being diverted to their detection and characterization.

‘Mainland-island’ population structure of a terrestrial salamander in a forest-bocage landscape with little evidence for in situ ecological speciation

“…Hardy-Weinberg equilibrium and linkage disequilibrium results were interpreted under the Benjamini-Hochberg correction for multiple comparisons. Statistical power for the detection of genetically differentiated yet sympatric populations was estimated following Jorde et al 64 . The genetic diversity among populations was summarized by clustering with the unweighted pair group method with arithmetic mean with Primer-e software (UPGMA 65 ) and by principal component analysis (PC) with Adegenet version 2.0.0 following the manuals 66,67 .…”

Can we rely on selected genetic markers for population identification? Evidence from coastal Atlantic cod

“…Similar phenomena of coexisting types have been described for coastal and migratory cod along northern Norway (Johansen et al, ; Kirubakaran et al, ; Sarvas & Fevolden, ; Westgaard & Fevolden, ), Iceland (Halldórsdóttir & Árnason, ), Greenland (Therkildsen et al, ), and Canada (Berg et al, ), and thus appear to be common for this species. Phenotypically cryptic, coexisting lineages or ecotypes may be common also in other species but may be under‐reported because their detection requires either highly informative markers or extensive sampling to detect the often weak statistical signals of heterozygote deficiency and admixture linkage disequilibrium (Jorde, Andersson, Ryman, & Laikre, ).…”

Success of alignment-free oligonucleotide (k-mer) analysis confirms relative importance of genomes not genes in speciation and phylogeny

“…On the other hand, the reproductive isolation necessary to prevent the blending of diverging incipient species can also be achieved, without geographical separation (i.e. sympatrically; [54,55]), by means of internal genomic changes that may not directly involve genes (see below).…”