Evolution and biogeography of New Zealand's longjaw galaxiids (Osmeriformes: Galaxiidae): the genetic effects of glaciation and mountain building

1. The biological impact of glaciation in Southern Hemisphere freshwaters is poorly understood. Several large rivers of eastern South Island, New Zealand, represent a mosaic of glaciated and non-glaciated regions, and are thus well-suited for studies of post-glacial recolonization.
2. We conducted mtDNA analyses of South Island's endemic non-migratory longjaw galaxiids Galaxias prognathus and G. cobitinis (Osmeriformes: Galaxiidae) to test hypotheses of post-glacial recolonization, and to assess the vicariant effects of Pleistocene mountain building.
3. We analysed the phylogeography of longjaw cytochrome b sequences from 38 sites in central South Island ( n  = 83). On the basis of our sampling it seems that G. prognathus and G. cobitinis have a parapatric distribution in the Waitaki River system, their disjunction broadly coinciding with three large post-glacial lakes. Waitaki clades of both species are deeply divergent relative to conspecific taxa in drainages to the north and south.
4. Tests for recent population growth – predicted under post-glacial expansion of G. prognathus – do not refute recent recolonization of streams above glaciated lakes in the Waitaki River drainage. The apparent absence of potential 'source' populations from non-glaciated regions suggests a post-glacial population decline for G. prognathus below the Waitaki lakes.
5. Molecular clock calibrations based on several freshwater vicariant events elsewhere in New Zealand supported the geologically-derived hypothesis of Waitaki–Canterbury drainage isolation approximately 300 ka.     

Geological subsidence, river capture, and cladogenesis of galaxiid fish lineages in central New Zealand

We used mtDNA and isozyme analysis of a freshwater fish, Galaxias divergens (Osmeriformes: Galaxiidae), to test a hypothesis of drainage evolution in South Island, New Zealand. Geological evidence indicates that the presently north-flowing Kaituna River branch of the Pelorus River system once flowed south into the Wairau River system. The subsequent flow-reversal is thought to have resulted from Pleistocene subsidence in central New Zealand. mtDNA sequence data corroborated this geological hypothesis: rivers draining into Pelorus Sound were found to retain a genetic lineage of G. divergens that is otherwise restricted to the Wairau River system and adjacent coastal drainages (based on current sampling). Other sampled drainages in northern South Island and southern North Island were found to house lineages that were highly divergent from the Wairau–Pelorus clade. Isozyme data yielded groupings based on fixed differences that were largely congruent with mtDNA clades. Standard molecular calibrations suggest that vicariant isolation of Pelorus and Wairau systems (drainage reversal) occurred in the mid-Pleistocene rather than the late Pleistocene as suggested by geology. Future multidisciplinary analyses will aim to improve our understanding of geological and molecular evolutionary rates.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88 , 367–376.     

Evolution of biological dispersal corridors through a tectonically active mountain range in New Zealand

Aim To assess the geological evolution and biogeographical implications of low mountain passes. In particular, we question the common biogeographical belief that major mountain belts form impervious physical barriers to biological dispersal, and that related taxa found on opposites sides of mountains are necessarily a result of vicariant tectonic processes. Location The Southern Alps of New Zealand form a long (500 km) narrow mountain belt at the oblique collisional Pacific–Australian tectonic plate boundary. High mountains were uplifted during the Pliocene (2–5 Ma) and uplift has continued to the present day. Methods We integrate previous work from several disciplines to obtain an overview of inter‐relationships between plate tectonic processes, geomorphology and biogeography along the main mountain barrier in New Zealand, and then extend this approach to other major mountain belts. Results The Southern Alps initially formed a barrier to at least some biological dispersal, including vicariant formation of separate species of freshwater non‐migratory galaxiid fish on either side. However, the high mountain barrier was breached in several places when passive transport of topography occurred, from the low‐erosion rain shadow on the eastern side towards the high‐erosion, high‐rainfall western side. This tectonic transport resulted in the capture of eastern rivers by west‐draining rivers, leaving low passes at the topographic divide. These low‐elevation corridors permitted biological dispersal across the mountains, although continued uplift raises these passes. A new set of passes has formed in the northern part of the mountains where younger faults are cutting across the older mountain topography. These potential dispersal corridors are becoming lower with continued erosion, and more common as the defining structures migrate southwards. Main conclusions Biological dispersal across the Southern Alps may be facilitated by numerous mountain passes, especially via the new passes formed by cross‐cutting faults. More low‐lying corridors existed than is readily apparent now, as old river capture‐related passes have been blocked by ongoing uplift. The dynamic mountain‐building and erosional environment typified by the Southern Alps occurs in all the world’s collisional mountain belts, such as the Andes, Himalayas, European Alps and North American Cordillera. Sister taxa occurring across mountain belts are not necessarily a result of vicariance driven by the rise of the mountains, as numerous passes may have permitted intermittent dispersal. The evolution of low passes may have been more prevalent than is currently appreciated, suggesting that topographically complex mountain ranges might be more effectively viewed as dynamic filters within a probability landscape rather than as static and impervious high‐altitude barriers to all but the rarest of biological dispersal events. In some cases, the biological disjunctions observed across mountains may more directly reflect habitat differentiation driven by orographic mountain development that has limited the probability of trans‐alpine dispersal success.     

Genetic structuring in Andean landlocked populations of Galaxias maculatus: effects of biogeographic history

Aim To test whether the genetic diversity of diadromous and landlocked populations of the small puyen Galaxias maculatus (known as jollytail in Australia and inanga in New Zealand) follow the same structuring patterns observed for migratory and non‐migratory species of the genus Galaxias. This work also aimed to test whether the genetic structuring of a group of populations could be predicted from differences in the geomorphologic history of the region they inhabit. Location Eight landlocked populations were sampled from cold‐temperate lakes in north‐western Patagonia. The study area could be split latitudinally into two sectors that differed in their geomorphology, each of them hosting four populations. The southern sector shows evidence of a higher degree of glacial coverage, and the lakes are probably remnants of a big proglacial palaeolake. Lakes in the northern sector, on the other hand, suggest no common origin. Results Significant genetic structuring was found among the studied populations (Θ = 0.188), being the highest value reported to date for the species. Significant correlation was found between genetic diversity and lake area and perimeter. Diversity also showed a slight latitudinal variation suggesting the presence of genetically distinct groups of populations. The comparison of populations from the two geographical sectors showed that those from the north had a higher diversity, more private alleles and strong structuring, while those from the south were less diverse and much more homogeneous. Main conclusions Non‐migratory populations of G. maculatus show much higher values of genetic structuring than those reported for diadromous populations. This follows the pattern seen when comparing migratory and non‐migratory species of Galaxias. This agrees with population genetics theory which predicts that restricted gene flow would result in greater among‐population divergence. Also, differences between northern and southern populations agreed with what was predicted by the geomorphologic history of the study area. During the Last Glacial Maximum ice cover in that region may have reduced the habitat of G. maculatus to a refuge with an impoverished gene pool. When the ice receded, leaving a great proglacial lake, that former population expanded and became fragmented after water levels descended. This resulted in present day lakes harbouring homogeneous populations with reduced diversity. The northern sector, in contrast, was less affected by glaciers, resulting in more geomorphologically stable lakes holding genetically diverse populations.     

Morphological variation in diadromous and landlocked populations of the spotted galaxias,Galaxias truttaceus,in Tasmania,south-eastern Australia

Synopsis A comparison of a suite of morphometric measurements and meristic counts of individuals of two landlocked lacustrine and two diadromous riverine populations of Galaxias truttaceus was carried out utilising both univariate and canonical variate analyses. Lacustrine fish had fewer dorsal and anal fin rays than did riverine fish. Differences were not as clear for gill rakers and vertebrae. Comparisons of serial counts were made with two derived lacustrine species, G. auratus and G. tanycephalus, also from Tasmania. Lacustrine G. truttaceus varied in the same direction as the derived species, relative to riverine G. truttaceus. From an analysis of 12 body measurements, the first canonical variate clearly separated lacustrine fish from riverine fish largely based on measurements associated with fins (pre-anal fin length, length of anal base, pre-dorsal fin length, maximum length of dorsal fin and inter-orbital width). An overall value for the correct classification of fish into groups based on locality was 84%. The percentage of fish classified into the wrong habitat (lake or stream) was much less than the percentage classified between localities within habitats. Overall morphological variation was greater between than within habitats. It is suggested that the differences in water movement and food type may in part account for the differences shown and that selective pressures peculiar to the lacustrine environment may be causing the lake populations to diverge from the riverine populations.     

Isozyme analysis of Galaxias species (Teleostei: Galaxiidae) from the Taieri River, South Island, New Zealand: a species complex revealed

We examined genetic differentiation among 23 samples of non-migratory river galaxias from 17 streams in the Taieri River system, South Island, New Zealand. Four major genetic types were found, two of which occur in narrow sympatry in one location. These were compared with topotypical material representing Galaxias anomalus from the Clutha system (Otago) and G. vulgaris from the Waimakariri system (Canterbury) in order to establish identity. Morphological examination of these four major genetic types revealed consistent concomitant differences. The results suggest that there are at least three species of river galaxias in the Taieri system: G. anomalus, G. vulgaris and at least one previously undescribed species. We propose that the genetic structuring and subsequent speciation of this group has been promoted by the absence of the marine juvenile phase that is found in five other members of the genus native to New Zealand. This structuring may be exacerbated by population fragmentation over the last century owing to the negative influence of introduced trout. The phylogenetic diversity within the river system mirrors the diverse flora and invertebrate fauna of the region, and has conservation implications that parallel those resulting from our improved knowledge of the New Zealand herpetofauna through the application of genetic analysis.     

Mitochondrial DNA phylogenetics of the Galaxias vulgaris complex from South Island, New Zealand: rapid radiation of a species flock

Mitochondrial control region sequence variation was examined in the Galaxias vulgaris complex, a group of freshwater-limited galaxiid fishes endemic to South Island, New Zealand. Phylogenetic analyses were used to test the monophyly of seven non-migratory ( G. vulgaris complex) and one migratory ( G. brevipinnis ) species. Newly-described taxa, some diagnosed on the basis of subtle differences in morphology, are associated with strongly monophyletic mtDNA lineages. Although the current taxonomy is supported generally, sequence data suggest that Southland G. anomalus should be attributed to G. gollumoides , whereas Southland and Stewart Island G. depressiceps represent a new southern lineage. Molecular clock calibrations suggest that migratory and non-migratory forms, separated by a maximum of 6·4% sequence divergence, diverged no earlier than the mid-late Pliocene. Biogeographical implications of high diversity (eight lineages) in the south (Otago-Southland) and low diversity (one lineage) in central South Island (Canterbury) are discussed. The unresolved relationships among species may reflect a rapid evolutionary radiation, essentially a star phylogeny.     

Hypothesis: the rate and scale of dispersal of freshwater diatom species is a function of their global abundance

We have analysed the geographical records of a representative selection of extant diatom species from a freshwater pond. The more often a species is recorded in the ecological literature, the greater is its apparent global distribution. One explanation is that the frequently recorded species are globally abundant, whereas species that are infrequently recorded are globally rare. We suggest a model in which random dispersal is the dominant force driving large-scale distribution of species, with the rate and scale of dispersal largely determined by global population size. Thus species that are locally rare or abundant are likewise rare or abundant worldwide. It is predicted that many of the rarer diatom species will, with additional sampling effort, be shown to have wide geographical distribution, but this requires intensive studies focused on revealing species that are normally cryptic. The argument in favour of endemic diatom species is untenable, because it is not possible to disprove their existence elsewhere in the biosphere.     

New Zealand phylogeography: evolution on a small continent

New Zealand has long been a conundrum to biogeographers, possessing as it does geophysical and biotic features characteristic of both an island and a continent. This schism is reflected in provocative debate among dispersalist, vicariance biogeographic and panbiogeographic schools. A strong history in biogeography has spawned many hypotheses, which have begun to be addressed by a flood of molecular analyses. The time is now ripe to synthesize these findings on a background of geological and ecological knowledge. It has become increasingly apparent that most of the biota of New Zealand has links with other southern lands (particularly Australia) that are much more recent than the breakup of Gondwana. A compilation of molecular phylogenetic analyses of ca 100 plant and animal groups reveals that only 10% of these are even plausibly of archaic origin dating to the vicariant splitting of Zealandia from Gondwana. Effects of lineage extinction and lack of good calibrations in many cases strongly suggest that the actual proportion is even lower, in keeping with extensive Oligocene inundation of Zealandia. A wide compilation of papers covering phylogeographic structuring of terrestrial, freshwater and marine species shows some patterns emerging. These include: east–west splits across the Southern Alps, east–west splits across North Island, north–south splits across South Island, star phylogenies of southern mountain isolates, spread from northern, central and southern areas of high endemism, and recent recolonization (postvolcanic and anthropogenic). Excepting the last of these, most of these patterns seem to date to late Pliocene, coinciding with the rapid uplift of the Southern Alps. The diversity of New Zealand geological processes (sinking, uplift, tilting, sea level change, erosion, volcanism, glaciation) has produced numerous patterns, making generalizations difficult. Many species maintain pre‐Pleistocene lineages, with phylogeographic structuring more similar to the Mediterranean region than northern Europe. This structure reflects the fact that glaciation was far from ubiquitous, despite the topography. Intriguingly, then, origins of the flora and fauna are island‐like, whereas phylogeographic structure often reflects continental geological processes.     

Genetic diversity and historical population structure in the New Zealand mayfly Acanthophlebia cruentata

1. Nucleotide sequences of a 280 base pair region of the cytochrome b gene were used to assess genetic diversity and to infer population histories in the New Zealand mayfly Acanthophlebia cruentata. 2. A hierarchial examination of populations from 19 streams at different spatial scales in the central and northern North Island of New Zealand found 34 haplotypes. A common haplotype was found in all central region streams and unique haplotypes in northern streams. Several central streams had region specific haplotypes with genetically differentiated populations at the 70–100 km scale. 3. Haplotype diversity was high (0.53–0.8) at most sites, but low (0–0.22) in some central sites. amova analyses found significant genetic diversity among regions (69%) and among catchments (58%). Most population pairwise F_ST tests were significant, with non‐significant pairwise tests among sites in the central region and pairs of sites between neighbouring streams. 4. The levels of sequence divergence are interpreted as the result of Pleistocene divergence in multiple refugia, leading to the evolution of regionally unique haplotypes. The low diversity in some central region populations may result from recent colonisation following local extinctions, associated with volcanic events.     

Genetic variation,population structure and cryptic species within the black mudfish,Neochanna diversus,an endemic galaxiid from New Zealand

To investigate the phylogenetic relationships and geographical structure among landlocked populations of the black mudfish, Neochanna diversus, mitochondrial DNA nucleotide sequence data were sampled from seven populations from the Waikato and Northland regions of New Zealand. The complete D-loop region was sequenced from 70 individuals, with 913 bp from the tRNA-pro end used in population and phylogenetic analysis. A tandem repeat array, which ranged in size up to 200 bp, was found in most populations at the 3′ end of the D-loop that was not able to be aligned for analysis. Of the seven sites sampled, two from Northland exhibited significant sequence divergence from all other sites. There was also a clear distinction among remaining Northland sites and those from the Waikato. An additional 518 bp segment of the 16S region was sequenced from all sites and compared with the other New Zealand mudfish species, N. apoda, N. burrowsius and the Tasmanian mudfish Galaxias (Neochanna) cleaveri using Galaxias maculatus as an outgroup. Both D-loop and 16S sequence data provided strong evidence for a cryptic species of mudfish present in Northland. The significant genetic structure apparent in the black mudfish appears most probably to be attributed to geological conditions during the Pliocene, where peat wetlands became apparent in the Waikato while Northland consisted of disjunct ‘islands’. Conservation and management of these populations must take into account the historical processes that have shaped these patterns of genetic diversity.     

Assessing the role of off‐take and source–sink dynamics in the extinction of the amphidromous New Zealand grayling (Prototroctes oxyrhynchus)

1. Some extinctions have obvious drivers (e.g. over‐harvesting), while others can be less obvious and arise from multiple interacting factors. The extinction of the New Zealand grayling (Prototroctes oxyrhynchus) has been blamed on over‐fishing and predation by introduced trout, but these explanations fail to account for the species disappearance from isolated, uninvaded rivers. We investigated if source–sink dynamics, facilitated by P. oxyrhynchus's amphidromous dispersal habit, could account for the species’ rapid extinction.
2. We created a database of P. oxyrhynchus sightings by surveying newspapers dating back to 1839, along with a review of traditional scientific literature. We used this database to update P. oxyrhynchus's known distribution map and inform sighting models to predict P. oxyrhynchus's extinction date. Finally, we implemented a meta‐population model to explore how source–sink dynamics could interact with off‐take (over‐fishing or predation) to drive extinction.
3. Prototroctes oxyrhynchus was found across New Zealand, except the north of the North Island. Based on sightings methods, the earliest predicted extinction date was 1924, although the species may have persisted until 1972, later than previous estimates have suggested. In the absence of source–sink dynamics, relatively high levels of off‐take were sustainable (up to 30% per generation). When the species was modelled as a panmictic meta‐population including 5% sink habitats, the sustainable off‐take rate was reduced to as low as 5% per generation.
4. Prototroctes oxyrhynchus was a widespread, abundant species that underwent rapid declines and ultimately went extinct. Previous attempts to explain this extinction have failed to account for the species extinction from isolated, pristine rivers. Our modelling shows that treating the species as a panmictic metapopulation and including source–sink dynamics rapidly increases the probability of extinction. We suggest that source–sink dynamics may be an important aspect of the population dynamics of amphidromous species and should be considered when managing taxa with similar dispersal habits.

     

Managing genetic diversity in threatened populations: a New Zealand perspective

Genetic diversity allows a population to adapt genetically to a changing environment or to buffer it against stochastic events such as harsh weather or disease outbreaks. Genetic diversity is therefore an important consideration in the development of management strategies for threatened populations around the world, with the possible exception of New Zealand, where species recovery programmes tend to focus on increasing population size while neglecting the maintenance of genetic diversity. Many of New Zealand?s threatened species have relatively low genetic variation and consequently may still be at risk in the long-term due to reduced resilience even if the effects of introduced predators were eliminated. The three main factors affecting genetic diversity – genetic drift, inbreeding and population subdivision – are processes that potentially impact on many of our locally threatened species, but their effects tend to occur over a considerably broader timescale than ecological effects, and as such are much more difficult to detect and ultimately to justify additional resource spending towards. Our message is that genetic management of New Zealand threatened species should not take priority over other management concerns such as controlling predators or improving habitat quality, but it needs more attention than it currently receives. We recommend that genetic diversity be a fundamental component in long-term management strategies for threatened species, and that such strategies are made explicit within the New Zealand Department of Conservation?s current species recovery plans so that the persistence of biodiversity becomes of key importance, as opposed to current approaches that seek solely to maximise representation.     

New Zealand Lepidoptera: Basic biogeography

Abstract

The composition of the New Zealand Lepidoptera fauna is briefly described, and affinities within Tortricidae analysed. Sixty-five genera are used to indicate four possible sets of relationships, but shortcomings of taxonomic interpretations are outlined. Except for species with a wide dispersal range (some 6% of the fauna) most show affinities consonant with terrane biogeography. The panbiogeographic methodology is a potent tool in systematics, giving direction to the research effort.     

When galaxiid and salmonid fishes meet–a family reunion in New Zealand

New Zealand's small freshwater fish fauna has been augmented by introductions of exotic species, primarily salmonids. Brown and rainbow trout have been successful and the chinook salmon has established anadromous populations. Although few explicit data are available, it appears that addition of large salmonids has had harmful impacts on some indigenous species, particularly several galaxiids; these appear to result from predation and competitive exclusion. Interactions may be chronic or catastrophic. It is difficult to determine causes of chronic interactions, many instances of which are likely to be occurring and escaping notice. Further, it is difficult to separate the effects of human-induced habitat deterioration from inter-specific interactions. Catastrophic interactions are much easier to observe but even here determining the nature of interactions and ascribing causes is fraught with difficulties.     

Global sampling reveals low genetic diversity within Compsopogon (Compsopogonales,Rhodophyta)

Twenty-five specimens of the freshwater red alga Compsopogon were collected from locations in North America, South America, Europe, Asia, Australasia and Oceania, and from an aquarium, with the goal of determining genetic diversity among specimens and ascertaining the number of phylogenetic species. Specimens were morphologically identified as having either the ‘caeruleus’ morphology, with regular polyhedral cortical cells, or the ‘leptoclados’ morphology, with irregular cortical cells with rhizoidal outgrowths. The ‘leptoclados’ morphology has been used by some researchers to distinguish the genus Compsopogonopsis from Compsopogon, or at least to distinguish C. leptoclados from other Compsopogon species. Sequence data for the rbcL gene and cox1 barcoding region were obtained for most specimens. In addition, SSU and partial LSU (barcode) rDNA were explored for a few specimens, but all sequences were identical. For the 25 newly generated and eight previously published rbcL gene data, there were seven unique haplotypes, but the sequence divergence was very low (≤7 bp, ≤ 0.7%). One haplotype was widespread, represented by 21 specimens from diverse locations in all regions sampled. Likewise, the 22 new and one previously published cox1 barcode region sequences yielded seven unique haplotypes with little sequence divergence (≤13 bp, ≤ 2.0%). One haplotype was widespread, being shared among 16 specimens from all regions. The combined molecular and morphological data showed no genetic differentiation between the ‘caeruleus’ and ‘leptoclados’ morphologies. The ubiquitous distribution of Compsopogon in tropical/subtropical regions and its low genetic variation are probably facilitated by the alga's ability to tolerate a wide range of stream conditions and its propagation via asexual spores. Given the findings of previous culture-based studies, morphometric research and field observations, coupled with the results of our study, we conclude there is only a single monospecific genus worldwide and that the species is correctly called C. caeruleus, since this is the oldest validly published name; all other previously described species of Compsopogon and Compsopogonopsis are synonyms.