On and off the rocks: persistence and ecological diversification in a tropical Australian lizard radiation

Abstract

BackgroundCongruent patterns in the distribution of biodiversity between regions or habitats suggest that key factors such as climatic and topographic variation may predictably shape evolutionary processes. In a number of tropical and arid biomes, genetic analyses are revealing deeper and more localised lineage diversity in rocky ranges than surrounding habitats. Two potential drivers of localised endemism in rocky areas are refugial persistence through climatic change, or ecological diversification and specialisation. Here we examine how patterns of lineage and phenotypic diversity differ across two broad habitat types (rocky ranges and open woodlands) in a small radiation of gecko lizards in the genus Gehyra (the australis group) from the Australian Monsoonal Tropics biome.ResultsUsing a suite of approaches for delineating evolutionarily independent lineages, we find between 26 and 41 putative evolutionary units in the australis group (versus eight species currently recognised). Rocky ranges are home to a greater number of lineages that are also relatively more restricted in distribution, while lineages in open woodland habitats are fewer, more widely distributed, and, in one case, show evidence of range expansion. We infer at least two shifts out of rocky ranges and into surrounding woodlands. Phenotypic divergence between rocky ranges specialist and more generalist taxa is detected, but no convergent evolutionary regimes linked to ecology are inferred.ConclusionsIn climatically unstable biomes such as savannahs, rocky ranges have functioned as zones of persistence, generators of diversity and a source of colonists for surrounding areas. Phenotypic divergence can also be linked to the use of differing habitat types, however, the extent to which ecological specialisation is a primary driver or secondary outcome of localised diversification remains uncertain.Electronic supplementary materialThe online version of this article (10.1186/s12862-019-1408-1) contains supplementary material, which is available to authorized users.

Crypsis and convergence: integrative taxonomic revision of the Gehyra australis group (Squamata: Gekkonidae) from northern Australia

“…The major mtDNA lineages were supported by Oliver et al (2019) as being evolutionarily independent when applying statistical delimitation methods to the exon capture data. However, most candidate taxa show low levels of morphological differentiation and non-overlapping distributions with other lineages from the same species complexes (Noble et al, 2018;Oliver et al, 2019). Furthermore, while mtDNA sampling was geographically extensive in these previous studies, the level of mtDNA divergence between some recognised and candidate taxa was moderate (Tamura-Nei distances lower than 10%), and lower than observed between at least some other species of geckos in the same biome that show evidence of gene flow between lineages Moritz et al, 2018;Oliver et al, 2019).…”

“…They are relatively large-bodied (to 95 mm snout-vent length) scansorial geckos that occupy arboreal and rocky habitats. Recent analyses of this group based on mtDNA and exon-capture datasets identified numerous divergent lineages or candidate taxa within the eight species currently recognised (Noble et al, 2018;Oliver et al, 2019). The major mtDNA lineages were supported by Oliver et al (2019) as being evolutionarily independent when applying statistical delimitation methods to the exon capture data.…”

“…Recent analyses of this group based on mtDNA and exon-capture datasets identified numerous divergent lineages or candidate taxa within the eight species currently recognised (Noble et al, 2018;Oliver et al, 2019). The major mtDNA lineages were supported by Oliver et al (2019) as being evolutionarily independent when applying statistical delimitation methods to the exon capture data. However, most candidate taxa show low levels of morphological differentiation and non-overlapping distributions with other lineages from the same species complexes (Noble et al, 2018;Oliver et al, 2019).…”

“…However, most candidate taxa show low levels of morphological differentiation and non-overlapping distributions with other lineages from the same species complexes (Noble et al, 2018;Oliver et al, 2019). Furthermore, while mtDNA sampling was geographically extensive in these previous studies, the level of mtDNA divergence between some recognised and candidate taxa was moderate (Tamura-Nei distances lower than 10%), and lower than observed between at least some other species of geckos in the same biome that show evidence of gene flow between lineages Moritz et al, 2018;Oliver et al, 2019). The sparse sampling of specimens in the exon capture dataset for each lineage, compared to that for mtDNA, also precluded detailed assessment of introgression at geographic boundaries between candidate taxa.…”

“…Within these two species complexes, there is sufficiently dense spatial sampling to allow for a thorough assessment of morphological and genetic diversity across their distributions in the AMT. In contrast, an assessment of G. robusta and G. borroloola is not possible at this time owing to fewer specimens available, especially at boundaries between lineages (Noble et al, 2018;Oliver et al, 2019). The G. australis complex ranges widely across the AMT (Wilson & Swan, 2017) and currently comprises one recognised species (Uetz, Freed & Hošek, 2019), but four candidate species of arboreal/generalist taxa (Noble et al, 2018).…”