Bully Gobiomorphus Research Articles

Hunger games: foraging behaviour and shelter use in fish under the context-dependent influence of parasitism.

Diseases, and the parasitic organisms that cause them, can impact aspects of ecosystems ranging from altering food web connectivity to population dynamics. Apart from interspecific interactions, parasites can affect how their hosts behave with conspecifics, such as during competition for resources. Fish are important hosts to a variety of parasite taxa that can, through physical impairment or invasion of sense organs, affect how they interact with conspecifics for food, territory, or mates. In New Zealand, the common bully Gobiomorphus cotidianus plays host to a variety of parasites, encysting throughout the body (Apatemon sp.) or residing within the eyes (Tylodelphys darbyi). We hypothesized that fish with lower levels of infection would secure territories closer to a food patch and be more likely to tolerate sharing that territory. Our experiments show that parasites infecting different areas may have variable impacts on how far the host positions itself from a food patch and the likelihood that it shares its territory. Fish with higher intensities of T. darbyi tended to be closer to the food patch, but Apatemon sp. did not show a similar pattern. Higher infection levels of both parasites were statistically associated with bullies being less likely to share territory. Further, bigger fish were less likely to share their territory at higher intensities infection, and we observed individual variation in a fish's response between trials. Our findings support that parasites matter in ecological interactions but also emphasize the context dependence of their effects.

Effects of point source discharges on common bully (Gobiomorphus cotidianus) along the Waikato River, New Zealand

ABSTRACT The common bully (Gobiomorphus cotidianus) was used as a bioindicator to assess the impacts of geothermal, bleached kraft mill effluent (BKME), sewage, and thermal discharges in the Waikato River, Northern New Zealand. A range of morphological and physiological parameters were measured to assess fitness in fish sampled upstream and downstream from these point sources. Isotopic signatures gave evidence that fish were resident at sites and showed a gradient corresponding to site-specific sources of carbon and nitrogen along the river. There were changes in the size range and age structure of the populations but, no physiological responses were detected. Limited impacts were observed on common bully health at individual discharge sites, or downstream where the river showed gradual deterioration in water quality, particularly nutrient enrichment, and increased turbidity. Despite the gradual deterioration in water quality no concomitant cumulative impacts were observed in common bully. Responses were largely local in nature, responding to point-source discharges. Population responses at the geothermal and BKME discharge sites warrant further study to investigate possible effects on fish recruitment.

Phenotypic, ecological, and genomic variation in common bully (Gobiomorphus cotidianus) populations along depth gradients in New Zealand’s southern Great Lakes

Depth gradients in lakes are often key drivers of population divergence and speciation in fishes. New Zealand has many deep lakes but no known profundal specialist fishes or cases of intralacustrine speciation. We sampled a native benthic fish, the common bully (Gobiomorphus cotidianus), from 5 to 90 m depth in four South Island lakes to test for morphological, ecological, or genetic differentiation associated with depth. Deeper fish consistently had narrower bodies, while other morphological traits showed variable relationships with depth. Carbon and nitrogen stable isotope values of fish increased with depth, largely tracking isotopic trends with depth of benthic invertebrate prey. Genotyping-by-sequencing showed some genome-wide differentiation between two of the lakes, but no evidence for within-lake genetic structuring along depth gradients. These results indicate that individual bullies associate with shallower or deeper habitats within their lifetimes, but we found no evidence of progress toward genetic divergence within lakes. The apparent lack of intralacustrine genetic divergence in New Zealand’s fishes may be explained by a combination of environmental factors and constraints intrinsic to its marine-derived freshwater fish fauna.

Risky business: influence of eye flukes on use of risky microhabitats and conspicuousness of a fish host.

A prerequisite for a parasitic manipulation to be considered adaptive is that it confers a fitness benefit to the parasite, such as increased transmission to another host. These manipulations can involve alterations to a wide range of host phenotypic traits, including microhabitat choice. Eye flukes of the trematode family Diplostomidae use fish as intermediate hosts and must be transmitted by predation to a piscivorous bird. In New Zealand, the diplostomid Tylodelphys darbyi infects the eyes of a widespread endemic freshwater fish, the common bully Gobiomorphus cotidianus. Within the eye, T. darbyi metacercariae achieve large sizes and move freely about the aqueous and vitreous humors of the eye. We hypothesized that higher intensities of T. darbyi would (i) cause bullies to show increased activity and spend more time moving about in open space (i.e., more conspicuous, risky microhabitat) and (ii) reduce their ability to compete for shelter with fish harboring lower infection levels. Our experiments showed that heavily infected fish were more active and spent more time in the open, although the effect was age-dependent, with immature fish displaying decreases in activity and time spent in the open with increasing intensities of infection. We also demonstrated that heavily infected female bullies have a lower probability of using shelter, but males show the opposite pattern. It is possible that using more risky microhabitats increases the likelihood of the fish being eaten by the parasite's predatory avian definitive hosts. However, our findings indicate that age- and sex-dependent effects call for a more nuanced interpretation.

Non-native fish as glochidial sinks: elucidating disruption pathways for Echyridella menziesii recruitment

A potential mechanism of global decline in freshwater mussel (Unionida: Bivalvia) abundance and diversity is disruption of their obligate parasitic life-cycle by non-native fish species, which may introduce novel interaction pathways that threaten unionid recruitment. We assessed three non-native fish (brown bullhead catfish, Ameiurus nebulosus; rudd, Scardinius erythrophthalmus; and goldfish, Carassius auratus) as glochidial hosts for the New Zealand freshwater mussel Echyridella menziesii to test the hypotheses that (i) non-native fish will have lower glochidial attachment rates than a native fish (the common bully Gobiomorphus cotidianus), and (ii) encystment rate will be lower on non-native species. We found that the non-native fish had significantly lower total glochidial attachment than the native control fish after infestation and did not produce ecologically significant quantities of juvenile mussels. This research supports the general assumption that non-native species are less suitable hosts of native freshwater mussels. However, confirming our findings in the field will indicate if removing non-native fish or enhancing native fish populations is recommended for conservation of E. menziesii populations in New Zealand.

Body Condition Peaks at Intermediate Parasite Loads in the Common Bully Gobiomorphus cotidianus.

Most ecologists and conservationists perceive parasitic infections as deleterious for the hosts. Their effects, however, depend on many factors including host body condition, parasite load and the life cycle of the parasite. More research into how multiple parasite taxa affect host body condition is required and will help us to better understand host-parasite coevolution. We used body condition indices, based on mass-length relationships, to test the effects that abundances and biomasses of six parasite taxa (five trematodes, Apatemon sp., Tylodelphys sp., Stegodexamene anguillae, Telogaster opisthorchis, Coitocaecum parvum, and the nematode Eustrongylides sp.) with different modes of transmission have on the body condition of their intermediate or final fish host, the common bully Gobiomorphus cotidianus in New Zealand. We used two alternative body condition methods, the Scaled Mass Index (SMI) and Fulton’s condition factor. General linear and hierarchical partitioning models consistently showed that fish body condition varied strongly across three lakes and seasons, and that most parasites did not have an effect on the two body condition indices. However, fish body condition showed a highly significant humpbacked relationship with the total abundance of all six parasite taxa, mostly driven by Apatemon sp. and S. anguillae, indicating that the effects of these parasites can range from positive to negative as abundance increases. Such a response was also evident in models including total parasite biomass. Our methodological comparison supports the SMI as the most robust mass-length method to examine the effects of parasitic infections on fish body condition, and suggests that linear, negative relationships between host condition and parasite load should not be assumed.

Effect of ramp length and slope on the efficacy of a baffled fish pass

This study evaluated the effect of ramp length and slope on fish passage over baffled ramps with 15° and 30° gradients. Three fish species indigenous to New Zealand were tested: the redfin bully Gobiomorphus huttoni, the common bully Gobiomorphus cotidianus and the inanga Galaxias maculatus with ramp lengths of 3, 4·5 and 6 m. As slope and ramp length increased, passage success rate decreased for G. maculatus and G. cotidianus. At a slope of 15°, both G. maculatus and G. cotidianus could pass all ramp lengths tested with the highest success rate on the 3 m ramp. As the gradient increased to 30°, G. maculatus could only pass the 3 m ramp, and G. cotidianus were incapable of passing any ramp. Gobiomorphus huttoni were the only test species capable of climbing the wetted margin of the ramps. Increasing ramp slope significantly reduced passage success for G. huttoni, but ramp length, up to the maximum used in this study, had no significant influence on successful passage.

Responses of three PIT-tagged native fish species to floods in a small, upland stream in New Zealand

Floods are an integral part of flowing river systems, yet our understanding of freshwater fish behaviour during floods is limited. In 2008, 67 redfin bullies (Gobiomorphus huttoni), 22 shortjaw kōkopu (Galaxias postvectis) and 29 kōaro (Galaxias brevipinnis) were tagged with passive integrated transponder (PIT) tags and monitored in a 100-m study reach before, during or after three floods. Detection patterns of tagged fish indicated that they may be displaced or may move to areas with large substrates during floods. Two individuals returned to the same locations during multiple floods, suggesting that previous experience may influence refuge selection for some individuals. While small changes in community composition occurred that could be attributed to concurrent habitat changes, overall a remarkable level of persistence of individual fish was observed in the tagged community.

Conservation breeding of Shortfin eels Anguilla australis and Giant kokopu Galaxias argenteus at Mahurangi Technical Institute using aquarium and aquaculture techniques

Mahurangi Technical Institute (MTI) operates a commercial fish hatchery that conducts aquaculture research, acts as a teaching tool for aquaculture students, breeds native fish for reintroduction projects, and for supply to zoos and public aquariums for display, as well as breeding selected introduced species for biological control of aquatic weeds throughout New Zealand. This research arm has a long and successful history in the breeding and rearing of a number of fish species, including New Zealand native threatened freshwater‐fish species. The Shortfin eel Anguilla australis, Giant kokopu Galaxias argenteus, Banded kokopu Galaxias fasciatus, Shortjaw kokopu Galaxias postvectis, Koaro Galaxias brevipinnis, Redfin bully Gobiomorphus huttoni, Common bully Gobiomorphus cotidianus, Giant bully Gobiomorphus gobioides, Cran's bully Gobiomorphus basalis, Freshwater shrimp Paratya curvirostris and Freshwater crab Amarinus lacustris have all been bred successfully at MTI. Of these native species, MTI has successfully closed the lifecycle of Giant kokopu, Banded kokopu, Cran's bully, Common bully, Freshwater shrimp and Freshwater crab. This paper focuses on work so far conducted to close the lifecycle of the Shortfin eel and the Giant kokopu.

Obituary: Bob McDowall (September 1939 ‐ February 2011): a key contributor to our understanding of Southern Hemisphere biogeography and the significance of marine dispersal

ISSN 1948‐6596 profiles obituary Bob McDowall (September 1939 ‐ February 2011): a key contributor to our understanding of Southern Hemisphere biogeography and the sig‐ nificance of marine dispersal It is with great sadness that I report the loss of Dr Robert (“Bob”) Montgomery McDowall, on Febru‐ ary 19 th , 2011. Bob was a key figure in the study of Southern Hemisphere biogeography and marine dispersal. After a childhood of fishing and freshwater activities with his parents, both of whom were also scientists, Bob completed a MSc on the ecol‐ ogy of redfin bully (Gobiomorphus huttoni) at Vic‐ toria University, Wellington, in 1962. Bob subse‐ quently joined the Fisheries Laboratory of the New Zealand Marine Department in 1963, study‐ ing Galaxias maculatus, the dominant contributor to the New Zealand whitebait fishery, and a spe‐ cies that probably ignited his interest in biogeog‐ raphy, much as its distribution had earlier in‐ trigued the likes of Charles Darwin. Bob was soon awarded a National Research Fellowship to study overseas, and started a PhD on galaxiid systemat‐ ics at Harvard University in 1965, in an environ‐ ment that included some of the foremost evolu‐ tionary biologists (Mayr) and biogeographers (Darlington) of the time. Bob completed his PhD in 3 years, a timeframe to be much admired even in this age, which enabled him to return to New Zea‐ land via Chile—for galaxiid collections, of course! Back in New Zealand, Bob became New Zealand’s foremost freshwater fisheries scientist, outlasting the names of several Government departments, prior to “retiring” from the National Institute of Water and Atmosphere Research (NIWA) in March 2000. However, like many a great scientist, retire‐ ment freed Bob from administrative burdens such that he was able to focus entirely on research. While predominantly employed as a fisher‐ ies biologist, Bob somehow managed to regularly publish biogeographic research. In this context, Bob focussed on the Southern Hemisphere “Gondwanan” distribution of galaxiid fishes, and also the influence of diadromy (migration be‐ tween the ocean and freshwaters) on species dis‐ tributions. In the period following the acceptance The late Bob McDowall in December 2010. Picture by Ainslie McDowall of plate tectonics, Bob was a dominant protago‐ nist for the retention of oceanic dispersal as a valid biogeographic hypothesis (McDowall 1978), particularly in taxa such as his diadromous Galax‐ ias maculatus, where conspecific populations broadly occupy temperate lowland catchments throughout the Southern Hemisphere, and larvae have been recorded 100’s of km out to sea (McDowall et al. 1975). Bob argued his point against several notable opponents within the dis‐ cipline: Nelson, Rosen, Platnick, Croizat. Much subsequent research has supported Bob’s position on oceanic dispersal, with many examples from terrestrial, freshwater, and nearshore marine fau‐ nas and floras (McDowall 2002; Sanmartin and Ronquist 2004; de Queiroz 2005). But while Bob could easily be considered a strong proponent of oceanic dispersal, it perhaps best reflects his at‐ tention to balanced approaches of scientific in‐ quiry, and in recent correspondence he was keen to highlight that Gondwanan vicariance should not be forgotten (fearing that the pendulum was now swinging too far the other way). Bob was a frenetic publisher, with (at last count) 267 scientific papers and 232 reports and popular articles. His papers spanned a variety of journals, including those not immediately within frontiers of biogeography 3.1, 2011 — © 2011 the authors; journal compilation © 2011 The International Biogeography Society

The missing host hypothesis: do chemical cues from predators induce life cycle truncation of trematodes within their fish host?

Using controlled experiments, the ability of the trematode parasite Stegodexamene anguillae, encysted within its intermediate fish host, the common bully Gobiomorphus cotidianus, was tested to indirectly detect the presence of its definitive host by exposing infected G. cotidianus to chemical cues from the definitive host, the short-finned eel Anguilla australis. The trematode can abbreviate its normal life cycle and achieve precocious maturity in G. cotidianus, or adopt the usual strategy consisting in delaying maturity until it reaches an A. australis. The results suggest that chemical cues from the definitive A. australis host do not affect the frequency of life cycle abbreviation in S. anguillae. Other life-history traits, such as parasite body size or the egg output of early-maturing parasites, were also unaffected by chemical cues from A. australis or from an alternative predator of G. cotidianus, the perch Perca fluviatilis, that is not a suitable host for the trematode. Therefore, factors other than A. australis host presence or abundance may be the important selective forces for life cycle abbreviation in this fish parasite.

Longitudinal size distributions of bluegill bullies (Gobiomorphus hubbsi) and torrentfish (Cheimarrichthys fosteri) in two large New Zealand rivers

This study compared the longitudinal size distribution of bluegill bullies (Gobiomorphus hubbsi) from Hutt River with existing data on the size distributions of bluegill bullies and torrentfish (Cheimarrichthys fosteri) from Rakaia River, New Zealand. All populations had longitudinal trajectories that showed some increase in size with distance upstream. This increase in size appeared to primarily reflect the influence of amphidromous life styles, where juveniles diffuse upstream from the sea. However, a quantile regression analysis revealed differences in growth and migration rate between the two bluegill bully populations; bluegill bullies from Rakaia River grew at a slower rate and showed variation in migration rate within their population that was not evident in the Hutt River population. Null models were also generated for each population to test for the presence of all size classes of fish in the lower reaches of each river. Both bluegill bully populations showed a significant absence of the largest size classes in the lower reaches and the size trajectories differed significantly from the null models. This difference suggests that all individual bluegill bullies continuously move upstream throughout their lives. In comparison, the size distribution of torrentfish closely resembled the null model, indicating that some individuals did not migrate upstream to the same extent as others.

Effects of riparian manipulation on stream communities in small streams: Two case studies

The effects of riparian manipulation in New Zealand are described for two case studies, one a short‐term study of the effects of the removal of riparian vegetation on fish, and the second, a long‐term study of the effect of re‐establishment of riparian vegetation on fish and benthic macro invertebrates. The first case study was an experiment carried out between November 2001 and May 2002. Overhanging bank vegetation and in‐stream wood were removed from short reaches of a small pastoral stream that had intact riparian margins, resulting in a change in stream structure with the formation of shallow uniform runs rather than pool and riffle structures as in unmodified reaches. The removal of bank cover and consequential instream habitat changes reduced inanga (Galaxias maculatus) densities by a factor of four within months of vegetation removal, showing the importance of instream cover and habitat to inanga. Adult longfin eel (Anguilla dieffenbachii) also became less abundant in the cleared reaches, but elvers (Anguilla spp.) became more abundant. In the second case study, pastoral sections in two small streams draining from native forest catchments were restored in 1995/96 by planting riparian vegetation and preventing stock access. After 10 years, the restoration efforts had more than doubled the numbers of giant kokopu (G. argenteus) and redfin bullies (Gobiomorphus huttoni), slightly increased numbers of banded kokopu (G. fasciatus), and decreased shortfin eel (A. australis) numbers by about 40%. The macroinvertebrate communities changed so that they became more similar to those at upstream native forest reference sites. These two case studies show that riparian margins can influence the composition of the fish and macroinvertebrate communities in small streams through the effects on cover, instream habitat and probably water temperature. Riparian restoration was most effective for the fish species that use cover and pool habitat.

Response of Gobiomorphus hubbsi (bluegill bully) to odours of conspecific fish in the presence of natural stream odours: Does habitat have an influence?

This study tested the ability of bluegill bullies (Gobiomorphus hubbsi) to detect and respond to the odour of conspecific fish upstream under neutrally odoured (rainwater) and naturally odoured (stream water) conditions. Bluegill bullies were presented with a choice of two flows of water to move into, one of which contained the odour of conspecific fish. Bluegill bullies displayed a concentration‐dependent reaction under neutral water conditions, where they were attracted to low concentrations of conspecific odour, but repelled by high concentrations of odour. This result was not consistent under naturally odoured water conditions, where no attraction towards conspecific odour occurred at low odour concentrations and only a weak avoidance of odour occurred at high concentrations. The differences revealed between natural and neutral water trials suggest the use of habitat odours over conspecific odours and cast doubt on previous studies only conducted under neutral conditions.

Spatial and temporal variation in the fish community of a South Island, New Zealand coastal lake

Communities in shallow coastal lakes are exposed to frequent environmental variation owing to their proximity to marine environments, and seasonal and daily variation in climate. Consequently, variability in these communities is likely to be considerable. The fish community of Lake Waihola, a shallow coastal South Island/New Zealand lake, was assessed by monthly day and night sampling by push net. A total of eight fish species were collected between January 1998 and January 1999. Common bully (Gobiomorphus cotidianus) comprised 78.92% of the total catch collected over the study period. Highest catches of common bully occurred inlate summer and autumn, mostly at night. Juvenile perch (Perca fluviatilis) were also caught in high numbers for a short period in mid‐summer, also mostly at night. Common smelt (Retropinna retropinna) and inanga (Galaxias maculatus) were collected in low numbers from late winter through to late autumn. Other species collected included shortfin eel (Anguilla australis), yellow‐eyed mullet (Aldrichetta forsteri), lamprey (Geotria australis), and black flounder (Rhombosolea retiaria). Variation in abundance was attributed to life history and ontogenic shifts in habitat use, and changes in habitat structure related to the development of submerged macrophyte beds during warmer summer periods.

Do toxic baits containing sodium fluroacetate (1080) affect fish and invertebrate communities when they fall into streams?

Large‐scale control of Australian possums throughout New Zealand uses toxic cereal baits containing 1080 (sodium fluoroacetate). These baits are often aerially applied over rough terrain where ground application is impractical. Many small streams flow in these areas, so 1080 baits can potentially fall into them. The ecological effect of 1080 leaching from baits was assessed on freshwater fish and invertebrate communities in four streams using a BACI experimental design. Four sites were selected in each stream: 10m and 100m below and 10m and 100m above where 1080 baits were placed. All sites were monitored 4 days and 1 day before and after baits were added, respectively. Separate experiments were conducted to assess impacts of 1080 on native fish and invertebrate communities. Baits were added to each stream to achieve bait densities 10 × greater than found after normal control operations. Three species of native fish, longfin eels (Anguilla dieffenbachii), koaro (Galaxias brevipinnis), and upland bullies (Gobiomorphus breviceps) were placed into separate cages at each site in each stream, and mortality monitored during the experiment. Analysis of water samples collected during the fish experiment showed that 1080 was detected only for 12h, and at low concentrations (c. 0.2 ìg litre‐1), despite the large number of baits placed in each stream. No fish died after addition of 1080 baits, suggesting that all three species were tolerant to dissolved 1080 at concentrations observed in this study. Invertebrate communities were quantified by sampling 10 replicate rocks at each site. Caddisflies (Helicopsyche, Pycnocentrodes, and Pycnocentria), orthoclad midges, and the mayfly Deleatidium dominated the community. 1080 had no detectable effects on the invertebrate community. These results suggest that 1080 leaching from submerged baits in small streams has no demonstrable biological impacts. Based on this finding, the need to maintain buffer zones around large waterways as some councils require is questioned.

Refuge‐use strategies of stream fishes in response to extreme low flows

Low flows were simulated in an artificial stream to determine the refuge‐use strategies of two benthic New Zealand fish species, Canterbury galaxias Galaxias vulgaris and upland bullies Gobiomorphus breviceps, and to investigate how refuge availability and the rate of flow recession affect the type and incidence of refuge use. When riffles dewatered, upland bullies tended to move to runs, whereas Canterbury galaxias showed a stronger propensity to burrow into the substratum. Both species showed a strong and consistent tendency to move upstream when emigrating from riffles. Burrowing was more frequent on coarse substrata and during rapid flow recessions. The incidence of surface stranding increased with the rate of flow recession, but only when interstitial refugia were unavailable, and was higher on gravel than on cobble substrata. The effect of rate of flow recession and substratum size on the probability of stranding depended upon the type of refuge‐use strategy adopted by the fishes. Rate of flow recession affected upland bullies more than Canterbury galaxias, whereas substratum size affected Canterbury galaxias more than upland bullies. These results suggest that the impact of disturbance is contingent upon species‐specific refuge‐use strategies, which result from interplay between refuge availability, the nature of the disturbance and species’ behaviours and morphologies. When component species adopt contrasting refuge‐use strategies, disturbance events may not consistently favour one species over another but rather inflict species‐specific mortality that varies both temporally and spatially.

RIVER CAPTURE, RANGE EXPANSION, AND CLADOGENESIS: THE GENETIC SIGNATURE OF FRESHWATER VICARIANCE

River capture is potentially a key geomorphological driver of range expansion and cladogenesis in freshwater-limited taxa. While previous studies of freshwater fish, in particular, have indicated strong relationships between historical river connections and phylogeographic pattern, their analyses have been restricted to single taxa and geological hypotheses were typically constructed a posteriori. Here we assess the broader significance of river capture among taxa by testing multiple species for the genetic signature of a recent river capture event in New Zealand. During the Quaternary an upper tributary of the Clarence River system was diverted into the headwaters of the Wairau River catchment. Mitochondrial DNA (control region and cytochrome b) sequencing of two native galaxiid fishes (Galaxias vulgaris and Galaxias divergens) supports headwater exchange: populations from the Clarence and Wairau Rivers are closely related sister-groups, whereas samples from the geographically intermediate Awatere River are genetically divergent. The upland bully Gobiomorphus breviceps (Eleotridae), in contrast, lacks a genetic signature of the capture event. We hypothesize that there is an increased likelihood of observing genetic signatures from river capture events when they facilitate range expansion, as is inferred for the two galaxiid taxa studied here. When river capture merely translocates genetic lineages among established populations, by contrast, we suggest that the genetic signature of capture is less likely to be retained, as might be inferred for G. breviceps. Rates of molecular evolution calibrated against this recent event were elevated relative to traditional estimates, consistent with the contribution of polymorphisms to branch lengths at shallow phylogenetic levels prior to fixation by purifying selection and drift.

RIVER CAPTURE, RANGE EXPANSION, AND CLADOGENESIS: THE GENETIC SIGNATURE OF FRESHWATER VICARIANCE

River capture is potentially a key geomorphological driver of range expansion and cladogenesis in freshwater-limited taxa. While previous studies of freshwater fish, in particular, have indicated strong relationships between historical river connections and phylogeographic pattern, their analyses have been restricted to single taxa and geological hypotheses were typically constructed a posteriori. Here we assess the broader significance of river capture among taxa by testing multiple species for the genetic signature of a recent river capture event in New Zealand. During the Quaternary an upper tributary of the Clarence River system was diverted into the headwaters of the Wairau River catchment. Mitochondrial DNA (control region and cytochrome b) sequencing of two native galaxiid fishes (Galaxias vulgaris and Galaxias divergens) supports headwater exchange: populations from the Clarence and Wairau Rivers are closely related sister-groups, whereas samples from the geographically intermediate Awatere River are genetically divergent. The upland bully Gobiomorphus breviceps (Eleotridae), in contrast, lacks a genetic signature of the capture event. We hypothesize that there is an increased likelihood of observing genetic signatures from river capture events when they facilitate range expansion, as is inferred for the two galaxiid taxa studied here. When river capture merely translocates genetic lineages among established populations, by contrast, we suggest that the genetic signature of capture is less likely to be retained, as might be inferred for G. breviceps. Rates of molecular evolution calibrated against this recent event were elevated relative to traditional estimates, consistent with the contribution of polymorphisms to branch lengths at shallow phylogenetic levels prior to fixation by purifying selection and drift.

Extensive genetic differentiation in Gobiomorphus breviceps from New Zealand

Partial mitochondrial DNA sequences for parts of the cytochrome b gene and control region were obtained for 89 upland bullies Gobiomorphus breviceps from 19 catchments in New Zealand. There were two highly distinctive mtDNA clades: a northern clade corresponding to the North Island, northern South Island and west coast South Island, and a south‐east clade, in the southern and eastern South Island. Within these major clades there were further distinct clades that correlated with geographic sub‐regions and catchments. The marked genetic differentiation has occurred in the absence of obvious morphological divergence. Based on cytochrome b sequence divergences and the molecular clock hypothesis, the northern and southeastern clades correspond with the uplift of the Southern Alps during the Pliocene, while populations in the North Island and northern South Island were estimated to have diverged during the Pleistocene. The widescale geographic divergences were similar to those observed in the galaxiids, Galaxias vulgaris and Galaxias divergens, but biogeographic management boundaries may not be the same, reflecting different evolutionary histories for non‐diadromous species occupying the same areas.