Temporal, spatial and ecological dynamics of speciation among amphi‐Beringian small mammals

Abstract

Aim Quaternary climate cycles played an important role in promoting diversification across the Northern Hemisphere, although details of the mechanisms driving evolutionary change are still poorly resolved. In a comparative phylogeographical framework, we investigate temporal, spatial and ecological components of evolution within a suite of Holarctic small mammals. We test a hypothesis of simultaneous divergence among multiple taxon pairs, investigating time to coalescence and demographic change for each taxon in response to a combination of climate and geography.Location Beringia, the nexus of the northern continents.Methods We used approximate Bayesian computation methods to test for simultaneous divergence among eight pairs of taxa, using cytochrome b gene sequences. We calculated coalescence times for eastern and western components of each pair and for the combined pairs, and relate dates to Quaternary climatic periodicity and combinations of environmental events and physical barriers. Population growth and expansion statistics were used to test evolutionary responses among taxa, including range shifts, persistence or periodic extirpation. Species distribution models (SDMs) for each taxon were used to predict their geographical ranges during the present interglacial, Last Glacial Maximum and previous interglacial.Results Multiple divergence events across Beringia were primarily coincident with extreme glacial cycles of the late Quaternary. Structure within Beringia is spatially consistent with at least three environmental barriers arising at different times: the Kolyma Uplands, Bering Strait and portions of the Bering Isthmus. Levels of divergence varied substantially, indicating evolutionary processes spanning deep and shallow time-scales. The different demographics among taxa reflect their distinct ecological responses. SDMs predicted regional distributional changes through time and different spatial responses among taxa.Main conclusions Beringia predominantly constituted a dispersal corridor during the early Quaternary and a major centre of endemism in the late Quaternary. Coincident with severe glacial cycles, small mammal species were 'caught' in Beringia and diversified over multiple climatic phases. Relative genetic differentiation across Beringia appears to be related to ecological differences reflecting a gradual adaptation to Beringian environments through time. Some methodological constraints associated with resolving recent (late Quaternary) isolation events or drawing inferences from a single locus are discussed.

Diversification of the cold-adapted butterfly genus Oeneis related to Holarctic biogeography and climatic niche shifts

“…Occurrences of all Arctic Oeneis species (Region C, Table S1) within Beringia support a primary refugial importance of this area for species survival (Yannic et al, 2014). Beringia was ice-free during the whole Pleistocene and served as refugium for mammals (Hope et al, 2013), plants (Eidesen et al, 2013) and other insects (Elias et al, 2000). Beringia could also represent another speciation centre for Oeneis butterflies, analogically to small mammals, which diversified in Beringia during glacial cycles by gradual adaptation (Hope et al, 2013).…”

“…Beringia was ice-free during the whole Pleistocene and served as refugium for mammals (Hope et al, 2013), plants (Eidesen et al, 2013) and other insects (Elias et al, 2000). Beringia could also represent another speciation centre for Oeneis butterflies, analogically to small mammals, which diversified in Beringia during glacial cycles by gradual adaptation (Hope et al, 2013). Further, we do not exclude the importance of smaller refugia outside of Beringia such as Siberia (Hope et al, 2010;Eidesen et al, 2013) for survival of some species/populations during the Pleistocene.…”

Hymenolepis folkertsi n. sp. (Eucestoda: Hymenolepididae) in the oldfield mouse Peromyscus polionotus (Wagner) (Rodentia: Cricetidae: Neotominae) from the southeastern Nearctic with comments on tapeworm faunal diversity among deer mice

“…Extensive diversification among species of Peromyscus occurred over the past 2 million years under episodes of habitat fragmentation linked to glacial-interglacial cycles and shifting climate during the Quaternary (e.g., Avise et al 1983;Dragoo et al 2006). The late Pliocene and Quaternary also coincided with considerable development and diversification of rodent faunas with temporally circumscribed episodes of expansion out of Eurasia into North America (Repenning 2001;Hope et al 2013). Episodic faunal mixing, cyclic isolation, and expansion may be reflected in the overall diversity of cestode faunas, assembled from multiple and disparate sources, and in the relatively depauperate and heterogeneous distributions that are now observed for hymenolepidids and other taxa among species of Peromyscus.…”

Toward a paradigm shift in comparative phylogeography driven by trait-based hypotheses

“…The insights provided by selecting one model over another will be limited if the models only vary in nonkey parameters that do not make any important difference for their biological interpretation (24). In other words, without knowing Box 1: Refined vs. Generic Hypotheses in hABC to Evaluate Climate-Driven Diversification hABC analyses are widely used in comparative phylogeography to evaluate scenarios of climate-driven diversification by testing for simultaneous divergence among population pairs of codistributed taxa (12,66,67). Here we highlight two case studies that applied hABC to island taxa to assess the hypothesized "species-pump" action of rising and falling sea levels under the Pleistocene Aggregate Island Complex (PAIC) (68) model of diversification, which is expected to produce a pattern of temporally clustered divergence times coinciding with high sea level periods (35) (Fig.…”