Delimiting cohesion species: extreme population structuring and the role of ecological interchangeability

Abstract

Species exhibiting morphological homogeneity and strong population structuring present challenging taxonomic problems: morphology-based approaches infer few species, whereas genetic approaches often indicate more. Morphologically cryptic, yet genetically divergent species groups require alternative approaches to delimiting species that assess adaptive divergence and ecological interchangeability of lineages. We apply such an approach to Promyrmekiaphila, a small genus (three nominal taxa) of trapdoor spiders endemic to northern California to define cohesion species (lineages that are genetically exchangeable and ecologically interchangeable). Genetic exchangeability is evaluated using standard phylogeographical techniques (e.g. nested clade analysis); ecological interchangeability is assessed using two GIS-based approaches. First, climatic values are extracted from layer data for each locality point and utilized in a principal components analysis followed by MANOVA. Second, niche-based distribution models of genetically divergent lineages are created using a maximum-entropy modelling approach; the amount of overlap among lineages is calculated and evaluated against a probability distribution of null overlap. Lineages that have significant amounts of predicted overlap are considered ecologically interchangeable. Based on a synthetic evaluation of ecological interchangeability, geographical concordance, and morphological differentiation, we conclude that Promyrmekiaphila comprises six cohesion species, five of which are cryptic (i.e. undetectable by conventional means).

Biological differences between two allopatric populations of Amblyomma cajennense (Acari: Ixodidae) in Argentina

“…The species concept has been largely discussed, and different definitions (biological, ecological, evolutionary and phylogenetic, among others) were proposed (Wheeler and Meier 2000;Stockman and Bond 2007). In these concepts, the delimitation of the species is based on a single criterion.…”

Gene trees, species and species trees in the Ctenosaura palearis clade

“…Delimiting species boundaries is an important, yet difficult, component of conservation biology as these are the units most often recognized and/or given protection through governmental and international agencies (Sites and Crandall 1997;Peterson and Navarro-Siguenza 1999;Sites and Marshall 2004;Stockman and Bond 2007). In conservation management, a pragmatic definition of ''species'' is a distinct group of organisms meriting independent legal status because extinction of such a group would constitute a substantial loss of biological diversity.…”

Delimiting species boundaries within the Neotropical bamboo Otatea (Poaceae: Bambusoideae) using molecular, morphological and ecological data

“…Following Phillips et al (2006), we used the default modeling parameters for all species with a logistic output. Binary maps (predicted presence or absence) were created from the Maxent-generated niche distribution models using the lowest presence threshold value (LTP) Stockman and Bond, 2007;Bond and Stockman, 2008).…”

“…Current research considers niche modeling to be useful for identifying and diagnosing species Rissler and Apodaca, 2007;Stockman and Bond, 2007;Bond and Stockman, 2008) and for finding potential new species (Raxworthy et al, 2003). Niche modeling is able to provide evidence for geographic isolation among populations (based on either conserved or divergent ecological niches) and takes populations to be separately evolving lineages when gene flow is considered unlikely for the intervening geographic regions (Wiens and Graham, 2005).…”