Genetic diversity and structuring across the range of a widely distributed ladybird: focus on rear‐edge populations phenotypically divergent

Abstract

Population genetics and phenotypic structures are often predicted to vary along the geographic range of a species. This phenomenon would be accentuated for species with large range areas, with discontinuities and marginal populations. We herein compare the genetic patterns of central populations of Coccinella septempunctata L. with those of two phenotypically differentiated populations considered as rear‐edge populations and subspecies based on phenotype (Algeria and Japan). According to the central‐marginal model and expected characteristics of rear‐edge populations, we hypothesize that these rear‐edge populations have (1) a reduced genetic diversity, resulting from their relative isolation over long periods of time, (2) a higher population genetic differentiation, explained by low contemporary gene flow levels, and (3) a relationship between genetic diversity characteristics and phenotypes, due to historical isolation and/or local adaptation. Based on genotyping of 28 populations for 18 microsatellite markers, several levels of regional genetic diversity and differentiation are observed between and within populations, according to their localization: low within‐population genetic diversity and higher genetic differentiation of rear‐edge populations. The genetic structuring clearly dissociates the Algerian and Eastern Asia populations from the others. Geographical patterns of genetic diversity and differentiation support the hypothesis of the central‐marginal model. The pattern observed is in agreement with the phenotypic structure across species range. A clear genetic break between populations of Algeria, the Eastern Asia, and the remaining populations is a dominant feature of the data. Differential local adaptations, absence of gene flow between marginal and central populations, and/or incapacity to mate after colonization, have contributed to their distinct genotypic and phenotypic characteristics.

Seminatural areas act as reservoirs of genetic diversity for crop pollinators and natural enemies across Europe

“…This study revealed a lack of genetic structure, very limited differentiation (F ST < 0.05), and a weak pattern of isolation-by-distance across populations sampled from Portugal to India. Only eastern Asia (China, Japan) and some North African populations (Algeria) were assigned to different genetic clusters and presented a significant genetic differentiation (F ST = 0.10-0.30), which suggests either long-term isolation of these peripheral populations (e.g., in different glacial refugia) or the evolution of reproductive isolation and an incipient process of cryptic speciation (Lecompte et al, 2016). In contrast, analyses for A. flavipes revealed a marked genetic structure and differentiation (F ST = 0.10-0.44) at a European scale, with more peripheral populations from Jutland (DK) and Iberian (ES) peninsulas forming distinct genetic clusters with limited gene flow between them as well as with the rest of analyzed populations (Figures 3 and 4).…”

“…Insects and other arthropods providing ecosystem services are often highly mobile organisms that disperse and forage across habitats in heterogeneous landscapes (e.g., Jaffé et al, 2016; Lecompte et al, 2016). This implies that their persistence and conservation does not only rely on local habitat quality but also on the landscape‐level habitat composition and configuration, in particular, connectivity between suitable habitats (Kremen et al, 2007; Martin et al, 2019).…”

Phenotypic Variation of Partridge Pea (Chamaecrista fasciculata) from Mississippi Persists in a Common Garden

“…Whereas the former experience loss of variation through founder events (Ibrahim et al 1996, Hewitt 2000, 2004, rear-edge populations may have low genetic variation due to genetic drift (Dynesius and Jansson 2000). If rear-edge populations remain isolated from conspecific populations, then there is a greater chance that they will become genetically and phenotypically distinct from central populations (Martin and Mckay 2004, Hardie and Hutchings 2010, Lecompte et al 2016). The contemporary distribution of partridge pea in the United States extends from the Gulf Coast northward to Minnesota and westward to Texas, but we have little understanding of its phylogeographic history.…”

An annotated checklist of ladybeetle species (Coleoptera, Coccinellidae) of Portugal, including the Azores and Madeira Archipelagos

“…Relatively important species in cereal crops in the Azores, especially in the first half of the 20 th century, having eventually disappeared when these crops became scarce (Soares et al 2008;Soares et al 2017). The taxonomic status of C. algerica has been under discussion because of its morphological similarities to the geographically widespread Coccinella septempunctata L. Although Lecompte et al (2016) revealed a high genetic structuring pattern, with an Algerian rear-edge population highly differentiated, consistent with their morphological distinctiveness, a recent study by Romanowski et al (2019) demonstrated that individuals from Canarian populations, usually classified as C. algerica, can hybridise with individuals from European populations of C. septempunctata giving rise to fertile F1 descendants. These authors therefore propose to synonymise C. algerica with C. septempunctata but, taking into account the morphological peculiarities of the North African and the Canarian populations, they consider that this species is a subspecies: Coccinella septempunctata algerica Kovář, 1977.…”