Glacial connectivity and current population fragmentation in sky islands explain the contemporary distribution of genomic variation in two narrow‐endemic montane grasshoppers from a biodiversity hotspot
Aim: Cold-adapted
biotas from mid-latitudes
often show small population sizes, harbour
low levels of local genetic diversity and are highly vulnerable to extinction due
to ongoing climate warming and the progressive shrinking of montane and alpine
ecosystems. In this study, we use a suite of analytical approaches to infer the demographic
processes that have shaped contemporary patterns of genomic variation
in Omocestus bolivari and Omocestus femoralis, two narrow-endemic
and red-listed
Iberian grasshoppers forming highly fragmented populations in the sky island archipelago
of the Baetic System.
Location: South-eastern
Iberia.
Methods: We quantified genomic variation in the two focal taxa and coupled ecological
niche models and a spatiotemporally explicit simulation approach based on
coalescent theory to determine the relative statistical support of a suite of competing
demographic scenarios representing contemporary population isolation (i.e. a predominant
role of genetic drift) versus historical connectivity and post-glacial
colonization
of sky islands (i.e. pulses of gene flow and genetic drift linked to Pleistocene
glacial cycles).
Results: Inference of spatial patterns of genetic structure, environmental niche modelling
and statistical evaluation of alternative species-specific
demographic models
within an approximate Bayesian computation framework collectively supported genetic
admixture during glacial periods and post-glacial
colonization of sky islands,
rather than long-term
population isolation, as the scenario best explaining the current
distribution of genomic variation in the two focal taxa. Moreover, our analyses
revealed that isolation in sky islands has also led to extraordinary genetic fragmentation
and contributed to reduce local levels of genetic diversity.
Main conclusions: This study exemplifies the potential of integrating genomic and
environmental niche modelling data across biological and spatial replicates to determine
whether organisms with similar habitat requirements have experienced concerted/idiosyncratic responses to Quaternary climatic oscillations, which can ultimately
help to reach more general conclusions about the vulnerability of mountain
biodiversity hotspots to ongoing climate warmingPeer reviewe