Multi-Island Endemicity: Phylogeography and Conservation of Coelus pacificus (Coleoptera: Tenebrionidae) Darkling Beetles on the California Channel Islands

Abstract

The California Channel Islands have been the focus of multiple conservation studies on charismatic vertebrates and plant species, but very few studies have focused on insects. In this study we examined the phylogeography of Coelus pacificus Fall (Coleoptera: Tenebrionidae), a dune-inhabiting darkling beetle, endemic to the islands. Our aim in this study is to decipher the relationships between C. pacificus and the congeneric species Coelus ciliatus Eschscholtz that is distributed on the mainland, to examine the biogeographic relationships of the islands and augment the conservation efforts on the islands with insect data. We sequenced 235 specimens of Coelus for the cytochrome oxidase I mitochondrial gene. We performed phylogenetic analyses to assess the historical relationships of the different species and islands. We also examined the connectedness of the islands by using pairwise φst and hierarchical analysis of molecular variance to test alternate hypotheses of geographical structure, Based on the phylogenetic analyses, C. pacificus is a valid, multi-island endemic species. Haplotypes were grouped into two clades: one clade composed of Santa Cruz, Santa Rosa, San Miguel, and San Nicolas; and the other clade composed of Santa Catalina and San Clemente. The highest haplotypic diversity was observed in San Clemente and San Nicolas islands, but all islands had unique haplotypes. Two haplotypes morphologically indistinguishable from C. pacificus formed a sister clade to C. ciliatus, suggesting either an ancient hybridization event or cryptic speciation. The California Channel Islands should be managed on a system wide basis, at least for some of the organisms or habitats and each island's population requires separate management to protect genetic integrity.

Phylogeography and genetic structure of endemic Acmispon argophyllus and A. dendroideus (Fabaceae) across the California Channel Islands

“…Riley and McGlaughlin (2016) found that incorporating the direction of prevailing and seasonal winds further enhances the predictive power of levels of plant endemism across the Channel Islands. Common genetic patterns in animals inhabiting these islands include relatively low divergence among populations on the northern islands (e.g., Gilbert et al, 1990; Ramirez and Beckwitt, 1995; Mundy et al, 1997; Landry et al, 1999; Coyer et al, 2008; Chatzimanolis et al, 2010), yet higher divergence between northern and southern islands (e.g., Ashley and Wills, 1989; Goldstein et al, 1999; Chatzimanolis et al, 2010).…”

Narrow water barriers prevent multiple colonizations and limit gene flow among California Channel Island wild buckwheats (Eriogonum: Polygonaceae)

“…Weissman & Rentz, 1976;Rust, 1985;Ramirez & Beckwitt, 1995;Chatzimanolis, Norris & Caterino, 2010), but have not received widespread attention. Frequent colonization of the northern islands combined with biotic or abiotic factors that favour southward expansion would also be expected to generate patterns of more diverse lineages on the northern islands and descendant lineages on the southern islands.…”

“…North-to-south patterns have been suggested among some invertebrate taxa (e.g. Weissman & Rentz, 1976;Rust, 1985;Ramirez & Beckwitt, 1995;Chatzimanolis, Norris & Caterino, 2010), but have not received widespread attention. Vertebrate phylogeographies do not support a general north-to-south colonization route, perhaps because of reliance on different dispersal mechanisms (i.e.…”

On the Origins of the Insect Fauna of California's Channel Islands: A Comparative Phylogeographic Study of Island Beetles

“…crassus, and Hy. lucidulus (as well as Coelus pacificus; Chatzimanolis et al 2010) pose a challenge for this hypothesis. If its biota truly is that recent, the island has supported exceptional diversification over a short span of geological time.…”