A Relaxed Molecular Clock Places an Evolutionary Timescale on the Origins of North American Big-Eared Bats (Vespertilionidae:Corynorhinus)

Characterization of the mitochondrial genomes of the Mexican endemic bats Corynorhinus mexicanus and Corynorhinus leonpaniaguae (Chiroptera: Vespertilionidae)

BACKGROUND

The genus Corynorhinus is composed of four recognized species: C. rafinesquii, C. townsendii, C. mexicanus, and C. leonpaniaguae, the latter two being endemic to Mexico. According to the IUCN, C. mexicanus is considered "Near Threatened", as its populations are dwindling and habitats are affected by anthropogenic disturbance. Corynorhinus leonpaniaguae has not been assigned to an IUCN Red List risk category due to its recent description.

METHODS AND RESULTS

In this study, the mitochondrial genomes of C. mexicanus and C. leonpaniaguae were assembled and characterized in detail. The mitochondrial genomes (mtDNA) of C. mexicanus and C. leonpaniaguae have lengths of 16,470 and 16,581 bp respectively, with a predominant nucleotide usage of adenine (31.670% and 31.729%, respectively) and thymine (26.15% and 26.18%, respectively). The mtDNA of C. mexicanus and C. leonpaniaguae is composed of 37 coding and non-coding elements: 22 transfer RNAs (tRNA), 13 protein-coding genes (PCGs), two ribosomal RNAs and a non-coding region, the control region, which has a length of 933 bp and 1,149 bp, respectively. All tRNAs exhibited a cloverleaf secondary structure, with the exception of trn-Ser1 which showed a deletion of the dihydrouridine arm in the two species. All PCGs are subjected to purifying selection, with atp8 being the gene showing the highest Ka/Ks value.

CONCLUSIONS

These are the first whole mitogenomic resources developed for C. mexicanus and C. leonpaniaguae and enhance our knowledge of the ecology of these species and aid in their conservation.

MC. Molecular and morphological data suggest a new species of big-eared bat (Vespertilionidae: Corynorhinus) endemic to northeastern Mexico

Corynorhinus mexicanus is an insectivorous bat endemic to Mexico that inhabits the high and humid regions of the Sierra Madre Oriental (SMO), the Trans-Mexican Volcanic Belt (TMVB), and the Sierra Madre Occidental (SMOC). A previous study suggested that C. mexicanus could be a cryptic species complex due to the genetic divergence observed between specimens from the TMVB and SMOC. The present study implemented phylogenetic, population genetics, and morphological analyses to evaluate the hypothesis that C. mexicanus is a species complex. The phylogenetic analysis indicated that C. mexicanus is a polyphyletic species composed of three indirectly related lineages. The estimated divergence times for the lineages suggest that they first originated during the Pliocene, while the second and third shared a common ancestor with C. townsendii 1.55 million years ago, and diverged 600,000 years ago during the Middle Pleistocene. The population genetics analysis reveals the SMO lineage of C. mexicanus is an isolated genetic group and highly diverged from the rest of lineages (SMOC and TMVB). The morphological analyses showed variation in the skull and mandible associated with the lineages and sex of the specimens, highlighting a difference in mandible shape between the specimens of the SMO and the rest of C. mexicanus. The results of this study suggest the presence of an undescribed species of the genus Corynorhinus.

Once upon a time in Mexico: Holocene biogeography of the spotted bat (Euderma maculatum)

Holocene-era range expansions are relevant to understanding how a species might respond to the warming and drying climates of today. The harsh conditions of North American deserts have phylogenetically structured desert bat communities but differences in flight capabilities are expected to affect their ability to compete, locate, and use habitat in the face of modern climate change. A highly vagile but data-deficient bat species, the spotted bat (Euderma maculatum), is thought to have expanded its range from central Mexico to western Canada during the Holocene. With specimens spanning this latitudinal extent, we examined historical demography, and used ecological niche modeling (ENM) and phylogeography (mitochondrial DNA), to investigate historic biogeography from the rear to leading edges of the species' range. The ENM supported the notion that Mexico was largely the Pleistocene-era range, whereas haplotype pattern and Skyline plots indicated that populations expanded from the southwestern US throughout the Holocene. This era provided substantial gains in suitable climate space and likely facilitated access to roosting habitat throughout the US Intermountain West. Incongruent phylogenies among different methods prevented a precise understanding of colonization history. However, isolation at the southern-most margin of the range suggests a population was left behind in Mexico as climate space contracted and are currently of unknown status. The species appears historically suited to follow shifts in climate space but differences in flight behaviors between leading edge and core-range haplogroups suggest range expansions could be influenced by differences in habitat quality or climate (e.g., drought). Although its vagility could facilitate response to environmental change and thereby avoid extinction, anthropogenic pressures at the core range could still threaten the ability for beneficial alleles to expand into the leading edge.