The Tarndale bully revisited with molecular markers: An ecophenotype of the common bullyGobiomorphus cotidianus(Pisces: Gobiidae)

Delayed adaptive radiation among New Zealand stream fishes: joint estimation of divergence time and trait evolution in a newly delineated island species flock

Adaptive radiations are generally thought to occur soon after a lineage invades a region offering high levels of ecological opportunity. However, few adaptive radiations beyond a handful of exceptional examples are known, so a comprehensive understanding of their dynamics is still lacking. Here, we present a novel case of an island species flock of freshwater fishes with a radically different tempo of adaptive history than that found in many popular evolutionary model systems. Using a phylogenomic data set combined with simultaneous Bayesian estimation of divergence times and trait-based speciation and extinction models, we show that the New Zealand Gobiomorphus gudgeons comprise a monophyletic assemblage, but surprisingly, the radiation did not fully occupy freshwater habitats and explosively speciate until more than 10 myr after the lineage invaded the islands. This shift in speciation rate was not accompanied by an acceleration in the rate of morphological evolution in the freshwater crown clade relative to the other species, but is correlated with a reduction in head pores and scales as well as an increase in egg size. Our results challenge the notion that clades always rapidly exploit ecological opportunities in the absence of competing lineages. Instead, we demonstrate that adaptive radiation can experience a slow start before undergoing accelerated diversification and that lineage and phenotypic diversification may be uncoupled in young radiations. [Adaptive radiation; Eleotridae; freshwater; Gobiomorphus; New Zealand.]

Phylogeography of the Cran’s bully Gobiomorphus basalis (Gobiiformes: Eleotridae) and an analysis of species boundaries within the New Zealand radiation of Gobiomorphus

New Zealand has a complex recent history of climatic and tectonic change that has left variable signatures in the geographic distribution and genetic structure of the region’s flora and fauna. To identify concordant patterns, a broad range of taxa must be examined and compared. In New Zealand’s North Island, a consensus is forming as to the dominant biogeographic barriers in the region although obligate freshwater taxa have not been considered in this framework. We use single-nucleotide polymorphisms to investigate phylogeography in the widespread obligate freshwater fish Gobiomorphus basalis on the North Island. Phylogeographic patterns within G. basalis reveal biogeographic disjunctions that are in some ways consistent and in other ways at odds with established patterns, providing insight into the processes that have shaped the islands’ biogeography. We also use phylogeography to delineate species boundaries within the entire New Zealand radiation of Gobiomorphus and find that it contains several morphologically cryptic species. We resolve two clades within G. basalis that correspond to areas north and south of the Taupo Volcanic Zone. We confirm the distinctiveness of Gobiomorphus alpinus relative to Gobiomorphus cotidianus, as well as the presence of two lineages within Gobiomorphus breviceps that were previously identified based on mitochondrial data.

Does fish ecology predict dispersal across a river drainage divide?

Obligate freshwater taxa are frequently distributed among catchments isolated by marine and terrestrial barriers. Such distributions can arise through vicariant changes in drainage geometry, or dispersal via intermittent freshwater connections. We employed two adjacent rivers in southern New Zealand to test for interdrainage dispersal while controlling for historical drainage geometry, and analyzed four ecologically distinct freshwater-limited fish taxa to assess any relationship with habitat preference. Individuals from the Mararoa and Oreti catchments (n >100 per species) were sequenced for a minimum of 1297 bp of mitochondrial DNA (cytochrome b and control region). Phylogeographic relationships were consistent with ecological expectations of interdrainage dispersal capability, with the two obligate riverine taxa each exhibiting reciprocal monophyly between catchments, whereas the two facultative swamp dwellers revealed paraphyletic relationships, one of which shared a haplotype between catchments. Statistical phylogeography, accommodating taxon-specific mutation rates and the known age of the last major riverine connection between these catchments, rejected complete isolation of populations for one of the swamp dwellers. Therefore, dispersal across a young (145-240 kyr) drainage divide is inferred for one species, and can be predicted to some extent by species ecology. Moreover, our study highlights the importance of historical drainage geometry when assessing the causes of contemporary genetic structuring in freshwater taxa.

Geological Dates and Molecular Rates: Rapid Divergence of Rivers and Their Biotas

We highlight a novel molecular clock calibration system based on geologically dated river reversal and river capture events. Changes in drainage pattern may effect vicariant isolation of freshwater taxa, and thus provide a predictive framework for associated phylogeographic study. As a case in point, New Zealand's Pelorus and Kaituna rivers became geologically isolated from the larger Wairau River system 70 to 130 kyr BP. We conducted mitochondrial DNA phylogeographic analyses of two unrelated freshwater-limited fish taxa native to these river systems (Gobiomorphus breviceps, n = 63; Galaxias divergens, n = 95). Phylogenetic analysis of combined control region and cytochrome b sequences yielded reciprocally monophyletic clades of Pelorus-Kaituna and Wairau haplotypes for each species. Calibrated rates of molecular change based on this freshwater vicariant event are substantially faster than traditionally accepted rates for fishes but consistent with other recent inferences based on geologically young calibration points. A survey of freshwater phylogeographic literature reveals numerous examples in which the ages of recent evolutionary events may have been substantially overestimated through the use of "accepted" calibrations. We recommend that--wherever possible--biologists should start to reassess the conclusions of such studies by using more appropriate molecular calibrations derived from recent geological events.