Historical biogeography of the arid-adapted velvet ant Sphaeropthalma arota (Hymenoptera: Mutillidae) reveals cryptic species


Correspondence and current address: Joseph S. Wilson, Department of Biology/MS 314, University of Nevada, Reno, NV 89557, USA.
E-mail: joe.s.wilson@gmail.com


Aim  To investigate the phylogeographic patterns among populations of the wide-ranging velvet ant Sphaeropthalma arota to (1) examine the biogeographic patterns within this species, and (2) associate major genetic divergences to historical vicariance events in order to gain insight into the processes that drove diversification in arid-adapted organisms.

Location  Western North America.

Methods  Phylogenetic relationships were determined by analysing the two ribosomal DNA internal transcribed spacers (ITS1 and ITS2) in MrBayes. Divergence dates were estimated for major nodes using two different molecular dating analyses: a penalized likelihood approach to rate smoothing using the program r8s, and a Bayesian MCMC averaging approach to rate smoothing using the program beast. Both analyses were calibrated using fossils from Dominican amber. Haplotype networks were estimated using tcs. Ecological niche models (ENMs) were developed using six bioclimatic variables from the WorldClim data set in the program Maxent.

Results  The phylogenetic reconstructions indicate that S. arota can be split into four deeply divergent lineages that probably represent distinct species. No morphological characters were found that can be used to identify these four species, making the S. arota species complex the first documented cryptic species complex in the family Mutillidae. Ecological niche models provide estimated distributions, which indicate that each of the four species inhabits a distinct niche. Divergence date estimates suggest that major diversification events occurred in the late Neogene.

Main conclusions Sphaeropthalma arota is composed of four genetically distinct species that cannot be distinguished morphologically based on current methods. We suggest that the members of this group be identified as the S. arota species complex. Major diversification events in this species complex can be linked to late Neogene mountain building and aridification events, specifically the uplift of the mountain ranges in southern California and the expansion of the Bouse Sea.