Boomeranging around Australia: Historical biogeography and population genomics of the anti‐equatorial fish Microcanthus strigatus (Teleostei: Microcanthidae)

Abstract

The geographic distributions of marine fishes have been shaped by ancient vicariance and ongoing dispersal events. Some species exhibit anti‐equatorial distributions, inhabiting temperate regions on both sides of the tropics while being absent from equatorial latitudes. The perciform fish Microcanthus strigatus (the stripey) exhibits such a distribution with disjunct populations occurring in East Asia, Hawaii, Western Australia, and the southwest Pacific. Here, we examine the historical biogeography and evolutionary history of M. strigatus, based on more than 80 specimens sampled from the four major populations. We analysed 36 morphological characters, three mitochondrial markers, and two sets of 7,120 and 12,771 single‐nucleotide polymorphisms from the nuclear genome. Our results suggest that M. strigatus represents a cryptic species complex comprising at least two genetically distinct populations worthy of species‐level recognition, with one population exhibiting strong genetic structuring but with intermittent, historical gene flow. We provide evidence for a southwest Pacific origin for the ancestral Microcanthus and explain how past connectivity between these regions might have given rise to the relationships observed in present‐day marine fauna. Our ancestral range reconstructions and molecular‐clock analyses support a southwest Pacific centre of origin for Microcanthus, with subsequent colonization of Western Australia through the Bass Strait followed by transequatorial dispersals to the Northern Hemisphere during the Pleistocene. Our results detail an anti‐tropical dispersal pattern that is highly unusual and previously undocumented, thereby emphasizing the importance of integrative systematics in the evaluation of widespread species.

Missing in the Middle: A Review of Equatorially Disjunct Marine Taxa

“…However, the majority of studies date divergence events between anti-tropical species to the Pliocene and Pleistocene (Bowen and Grant, 1997;most datasets used in Burridge, 2002;Hilbish et al, 2000;Mabuchi et al, 2004;Poortvliet et al, 2013;Hoover et al, 2017;Beldade et al, 2021). Intra-specific anti-tropical species (those with populations in both hemispheres) interestingly have also been found with varying divergence dates, ranging from the Miocene in some species (Veríssimo et al, 2010;Herrera et al, 2012), to the last 100,000 years (Tea et al, 2019). While the oldest intra-specific divergence dates likely represent distinct species (discussed in Veríssimo et al, 2010 andSchwaninger, 2008), additional intra-specific population genetic studies are needed across a variety of taxa.…”

“…Yet, at broader taxonomic scales an inverse latitudinal diversification gradient, with higher speciation rates outside of the tropics, has been observed in marine fishes (Rabosky et al, 2018), which runs counter to the biotic exclusion hypothesis. While these broad patterns may not strictly apply to all temperate taxa, ancestral area reconstructions focusing specifically on antitropical fishes like sawtail surgeonfishes and stripeys, and also herbivorous sea chubs that are a mix of temperate and tropical species, have suggested species origination in temperate areas, not tropical ones Knudsen et al, 2019;Tea et al, 2019). While this runs counter to one of the assumptions of the biotic exclusion hypothesis, suggesting that it might not apply to all anti-tropical taxa, the occurrence of contemporary suitable abiotic habitat in the tropics across a wide diversity of anti-tropical fishes suggests that biotic exclusion may be a plausible explanation for some taxa (Ludt and Myers, 2021; see discussion below).…”

DNA reconciles morphology and colouration in the drunk blenny genus Scartichthys (Teleostei: Blenniidae) and provides insights into their evolutionary history

“…The authors thus chose to use an informative prior for the evolutionary rate of COI of 1.2 × 10 −8 substitution per site per years commonly used for fishes for this marker ( e.g . Bermingham et al ., 1997; Lessios, 2008; Tea et al ., 2019). They assumed a strict clock for each of the six markers, with the relative rates of ENC1, myh6, ptr, sreb2 and tbr1 being inferred in the analyses of this study.…”

Distinguishing between dispersal and vicariance: A novel approach using anti‐tropical taxa across the fish Tree of Life

“…Species that recently underwent taxonomic splitting were also removed from the Randall (1981) species list because divergence times are not yet constrained to the Quaternary timeline of our hypotheses. One notable exception to this is Microcanthus strigatus , which was recently split longitudinally, but still maintains an anti‐tropical distribution that was formed during the Pleistocene (Tea & Gill, 2020; Tea et al., 2019). For the remaining taxa, distribution records were gathered from the Global Biodiversity Information Facility using the package ‘rgbif’ in R (Chamberlain et al, 2017).…”