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.     

中国不同地区标明剑线虫种内群体的形态学变异

通过对国内14省(市)1599份土壤样品的分离及鉴定,在北京、山东、山西、河北、河南、四川、浙江、福建、海南、重庆等10个省区的样品中发现63个标明剑线虫群体,占检测到剑线虫属群体总数的19.0%,表明该线虫为中国剑线虫属的优势种群之一,其中海南省为标明剑线虫新记录省。通过对采自海南、山东、四川、浙江四省份的标明剑线虫代表性群体的形态测量值比较,明确了标明剑线虫的雌虫齿针长、尾长、V值等主要形态测量值在种内群体间甚至群体内存在较大的变异范围,并在一定范围内出现重叠,但相互之间没有相关性。否认了将标明剑线虫分为二型(印度型和标明型)的说法。从杭州的一个标明剑线虫群体中发现了所有的四个幼虫龄期标本,并进行了详细的形态学观察和测量,其中有关该线虫的一龄幼虫为国内首次报道.     

Comparison of Day and Night Fyke Netting, Electrofishing and Snorkelling for Monitoring a Population of the Threatened Golden Galaxias (Galaxias auratus)

The littoral zone of small off-stream water storage containing a translocated population of Galaxias auratus was sampled fortnightly at day and night with fyke nets, electrofishing and snorkelling over 3 months. Variation in population data provided by each method, including relative abundance indices, size structure, and habitat preferences, were examined. Aspects of behaviour and activity patterns were also investigated. Night sampling using all methods consistently yielded larger catches than day sampling. The size structure of catches varied, with electrofishing at night and fyke netting during the day having higher proportions of juveniles, whilst snorkelling at night and electrofishing during the day had higher proportions of adults. Fyke netting at night yielded by far the largest catches (~3-fold more than other methods) and also captured balanced proportions of juveniles and adults. Galaxias auratus had a strong diel activity pattern and were most active at night. The majority of the population migrated into the littoral zone during the night and back into deeper water during the day. A small number of juveniles remained in the littoral zone and some adults sheltered in the dense cover of species-rich littoral vegetation during the day. Shores with shallow depth profiles appeared to be preferred due to higher catches in these areas using all methods. Based on the results of this study, fyke netting at night in littoral habitats is recommended for monitoring populations of G. auratus. Fyke netting is likely to be an effective method for monitoring other lacustrine galaxiid species; however, further work is required to investigate the effects of habitat variables and fish community structure on activity patterns of galaxiids, and hence their catchability with various methods, in more extensive lentic environments.     

The composition and importance of the phytoneuston in two floodplain lakes in south-eastern Australia

Normans Lagoon and 3-Gum pond are small floodplain water bodies adjacent to the Murray River, south-eastern Australia, and often have a visible film/sheen across their surface. Since few studies have provided quantitative comparisons of the surface and subsurface layer communities of shallow freshwater lakes, we determined the contributions of the surface and subsurface populations to overall algal biomass when a surface film was visible, and when it was not visible. We examined the algae and cyanobacteria present at the air–water interface of each water body, and compared the findings with those for the water immediately below the surface, and for the overall water column. The algal groupings Trachelomonas spp., other Euglenophyceae (principally Euglena spp.), Chlorophyceae and Cyanobacteria usually comprised >95% of the measured biovolume within all samples. Samples from the air–water interface were considerably enriched (up to 200-fold) with respect to algal biovolume, whether or not a visible surface film was present, and elevated cell counts were observed within the air–water interface for motile organisms such as Trachelomonas spp. and green unicellular flagellates. The reverse was true for the cyanobacterium Planktolyngbya however, with greater concentrations occurring at depth. In terms of its contribution to the overall algal/cyanobacterial populations within each water body, the surface layer was found to be responsible for <1–20% of the biovolume over the entire water column. Multivariate statistical analysis confirmed there were significant differences between the communities of the air–water interface and those of the water below, and that these differences occurred both in the presence and absence of a visible surface film/sheen. Handling editor: D. Ryder     

Microsatellite variation in natural Drosophila melanogaster populations from New South Wales (Australia) and Tasmania

Microsatellite variation was studied at 48 microsatellite loci in 10 Drosophila melanogaster populations to investigate the population structure on the Australian east coast. Low, but statistically significant population differentiation was observed among most populations. The populations on the Australian mainland did not show evidence for isolation by distance. We conclude that the population structure of D. melanogaster on the Australian mainland is probably the result of a shared history (recent colonization). The observed differences between local D. melanogaster populations probably reflect variation in effective population sizes rather than patterns of gene flow. Two populations from Tasmania were more differentiated from the Australian mainland than a population from Israel, raising the question whether they are derived from the Australian mainland or colonized from a different source population.     

Distribution and biology of Galaxias truttaceus (Galaxiidae) in south-western Australia, including first evidence of parasitism of fishes in Western Australia by Ligula intestinalis (Cestoda)

The freshwater trout minnow, Galaxias truttaceus, is restricted to the small catchments of the Goodga and Kalgan Rivers in Western Australia. Its large geographic separation from populations in south-eastern Australia, and subsequent reproductive isolation and variation in the prevailing environmental conditions, has created marked differences in biology (and morphology) between the eastern and western populations of G. truttaceus. The biology (spawning period, longevity, growth rates, diet and parasitism) of G. truttaceus in the Goodga River is described and then compared with information on the biology of diadromous and landlocked populations in south-eastern Australia (i.e. Tasmania) (see Humphries 1989). In the Goodga River, ca. 34 and 8% of males and females, respectively, attain maturity at the end of their first year, while only four mature males and one mature female 0+ fish were found in the Tasmanian populations. Adults migrate upstream prior to spawning which peaks during April and May. Larvae, which hatch at ca. 6.5mm (cf. 7.5–9.0mm in Tasmania), move downstream into Moates Lake for a few months before re-entering the river. Of the 810 G. truttaceus collected, ca. 53, 34, 10, 2, 1, 0.2 and 0.1% belonged to the 0+, 1+, 2+, 3+, 4+, 5+ and 7+ age classes, respectively. In contrast, the Tasmanian populations have a much higher proportion of older fish. At the end of their first, second and third years, the males on average attain 60, 84 and 95mm total length (TL), respectively, whereas females attain 63, 89 and 103mm TL, respectively at those ages. Only one fish > 140mm TL was captured, which contrasts with the Tasmanian fish, where a substantial proportion are > 140mm TL. The diet of fish > 40mm TL consisted of between 65 and 96% terrestrial fauna (mainly coleopterans and hymenopterans) in the different seasons. Larval fish diets were largely comprised of copepods.The occurrence of the introduced cestode Ligula intestinalis in ca. 7% of G. truttaceus represents the first record of this parasite in Western Australia. It was found to cause gonadal retardation and gross morphological deformities, the latter of which possibly increases the risk of avian predation.     

Extreme levels of intra-specific divergence among Cape Peninsula populations of the Cape galaxias,Galaxias zebratus Castelnau 1861, reveals a possible species complex

The Cape galaxias, Galaxias zebratus, is part of the paleao-endemic fauna characteristic of the south-western Cape, South Africa, and is the only galaxiid found in continental Africa. A 284-bp fragment of the cytochrome b region of the mtDNA was sequenced from 48 individual galaxiids, representing 10 populations from the Cape Peninsula. Five sequences, for four additional populations sampled at the extremes of the species range, were obtained from the literature. Analysis of cyt b mtDNA from these 14 populations of G. zebratus revealed five distinct and highly divergent lineages with low levels of intra-population mtDNA haplotype diversity. A new and distinct genetic lineage is described from the southern part of the Cape Peninsula. Estimates of genetic divergence between populations ranged from <1% to >17%. The observed level of sequence divergence represents the largest yet reported for any single fish species. The distribution of these lineages and their degree of sequence divergence refutes a model of isolation by distance. Results suggest that periods of low sea level may have been important in creating opportunities and alternative routes for dispersal and migration for Cape Peninsula populations.     

Hybridization of Cyprinus carpio and Carassius auratus,the first two exotic species in the lower Laurentian Great Lakes

Synopsis A preliminary comparison of Cyprinus carpio × Carassius auratus hybrids with the parent species is made by means of hybrid indices for 29 morphometric and 19 meristic characters. Of these 48 characters 29 were intermediate, seven were identical with one of the parents and 12 were extreme. Marked osteological differences in the crania of the parent species were noted as possible diagnostic characters for the identification of hybrids.Note     

Intraspecific variation in diet, growth, and morphology of landlocked Galaxias maculatus during its larval period: the role of food availability and predation risk

Food availability and predation risk have been shown to affect phenotypes during early life history of fishes. Galaxias maculatus, a small fish widely distributed around the southern hemisphere, clearly exhibits a complex trade-off between feeding and predation avoidance during growth over the larval period. We studied the effect of different environmental variables on diet, growth, mortality, and morphology through field surveys and data revision in the literature for limnetic G. maculatus larvae in five oligotrophic lakes of Patagonia. Both number of food categories and prey ingested by larvae were directly related to zooplankton density. Larval growth rate was related with zooplankton density and temperature. Lakes with high zooplankton densities and low predation risk had larvae with deeper bodies and shorter caudal peduncles, while in lakes with less food and high predation risk larvae were slender with shallower bodies and longer peduncles. Food availability and predation risk seem to operate on the swimming performance of G. maculatus larvae through the slenderness of the body and the length of the caudal peduncle. The observed phenotypic variation in growth and morphology could be a key feature that has allowed this species to successfully colonize a wide variety of environments in the southern hemisphere.     

Population structure and biology of alewives (Alosa pseudoharengus) and blueback herring (A. aestivalis) in the Saint John River,New Brunswick

Synopsis Examination of more than 2,000 alewives (Alosa pseudoharengus) and blueback herring (A. aestivalis) from various areas in the Saint John River, N.B., showed differences in their morphometric and meristic characters. They differed also in length and age, compositions, spawning time, length and age at maturity, back-calculated lengths, and growth parameters. Within each species, between-area comparisons showed significant differences in some of their meristic characteristics.To test a homing hypothesis for alewives, a multivariate analysis was performed on eight meristic characters. Two discriminant function programs, discriminant analysis for two groups and a multiple group stepwise discriminant analyses were used. Values of the generalized Mahalanobis D² and percent overlap in frequency distributions of meristic characters suggest that considerable straying of fish, especially between adjacent areas occurs during upstream spawning migration.This article is one of several papers presented at the Second European Ichthyological Congress, Paris, 8–15 September 1976, to be published in Environmental Biology of Fishes.     

Evidence of iteroparity in the widely distributed diadromous fish inanga Galaxias maculatus and potential implications for reproductive output

Gaps in understanding variability among populations of inanga Galaxias maculatus in the timing of reproduction were addressed in southern New Zealand (NZ), where G. maculatus constitutes a declining fishery. Reproductive activity was delayed by 1 month on the west coast compared with the east coast and the west coast spawning season was prolonged into winter. The evidence for post‐spawning survival of some fish was unequivocal from histological studies. These older and larger fish contributed disproportionately to egg production. Estimates of fecundity were considerably lower than those previously calculated for NZ populations. The importance of quality habitats being available during critical life history periods are highlighted. It was apparent that some streams supported fish that were larger and in better condition and that this translated into greatly increased fecundity. Future research should focus on whether this is a legacy of these fish experiencing better pre‐settlement marine habitat as larvae, or higher quality instream habitat enhancing the growth and development of adults.     

Colony cycle in the south-eastern coastal populations of Ropalidia plebeiana, the only Ropalidia wasp occurring in temperate Australia

Of the 22 species of Ropalidia occurring in Australia, only R. plebeiana is distributed in temperate areas. This wasp is abundant in the south‐eastern coastal regions of Australia, where it forms huge nest aggregations. Based on our observations in late autumn and early spring, as well as information in the literature, we outline the colony cycle of R. plebeiana in the south‐eastern coastal area of New South Wales. The nesting period lasts for approximately 9.5 months, which is unusually long for temperate polistine wasps. Most foundresses seem to return to their natal nests in early spring (mid‐August to early September) to start their own colonies by reusing pre‐existing nest combs, and the pre‐emergence stage (before the emergence of the first adult brood) lasts for approximately 3.5 months. Reproductives (gynes and males) start to emerge as adults in early March, and the reproductive‐producing period lasts until the end of May. Both the pre‐emergence stage and the reproductive‐producing period are much longer than in other temperate polistine wasps, which is discussed in terms of fluctuating temperature conditions in the area and the formation of nest aggregations, a peculiar habit for temperate populations of R. plebeiana.     

Effects of ultraviolet radiation on the eggs of landlocked Galaxias maculatus (Galaxiidae, Pisces) in northwestern Patagonia

• 1 Ultraviolet radiation (UVR) damages early life stages of several fish species. Galaxias maculatus is a small catadromous fish, with landlocked forms occurring in many lakes within the Nahuel Huapi National Park (Patagonia, Argentina). In this work, the vulnerability of G. maculatus eggs exposed to both natural and artificial UVR was investigated in relation to water transparency.
• 2 Field experiments were performed in two lakes differing in UVR attenuation. Galaxias maculatus eggs were exposed to in situ levels of UVR in quartz tubes incubated at various depths. For laboratory experiments, the eggs were exposed to five levels of artificial UVB radiation.
• 3 Exposure to natural UVR causes various degrees of egg mortality depending on water transparency and incubation depth. In the less transparent lake (K_d320 = 3.08 m^‐1), almost complete mortality was observed near the surface. At a depth of 43 cm the observed mortality was only 22%, but was still significantly different from the dark control. In the most transparent lake (K_d320 = 0.438 m^‐1), almost total mortality was observed in tubes incubated at 2.56 m or shallower. A gradual decline in mortality was recorded from that depth to 3.78 m where the values approached those in the dark control treatments.
• 4 A monotonic relationship between mortality and UV exposure could be observed both in field and laboratory experiments. Using the results from field incubations, a LD₅₀ of 2.5 J cm^‐2 nm^‐1 was estimated. In a few mountain lakes, this value would be exceeded even if the eggs were laid at the maximum depth of the lake. Thus UVR seems a sufficient cause to explain the absence of G. maculatus populations in some mountain lakes. For most lakes, however, UVR is probably one of several important environmental factors, which together determine the habitat suitability.

     

Disturbance,fish, and variation in the predatory insect guild of coastal streams

Species distributions, and thus the composition of communities, are determined by many interacting biotic and abiotic factors. We analyzed the variation in composition of the invertebrate predator guild across eight small, steep coastal streams in eastern Canada, in relation to variation in several broad categories of environmental variables: disturbance-related physical characteristics, top-down effects (fish), and bottom-up effects (prey composition and productivity-related physical/chemical variables). Similarity in composition (relative and absolute abundances of the 19 species belonging to the Rhyacophilidae, Perlodidae, and Chloroperlidae) declined significantly with distance. Streams that were most similar in predator composition were also most similar in physical factors related to disturbance, but were not more similar in prey abundance/composition or in environmental factors associated with productivity (chemistry, canopy cover, and riparian forest type). Similarity in the relative abundance of species within the Rhyacophilidae was linked to variation in the presence/abundance of brook trout. These results suggest that the invertebrate predator guilds of these small coastal streams are structured first and foremost by factors associated with the magnitude and variability of the flow regime, and second by response to top-down factors (predation by brook trout). There was no evidence that bottom-up effects altered the composition or abundance of the predator guild. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: Sonja Stendera     

Biology of the western minnow,Galaxias occidentalis Ogilby (Teleostei : Galaxiidae), in a south-western Australian river

The size and age composition, growth and diet of the western minnow, Galaxias occidentalis, in the southern branch of the Collie River in south-western Australia were determined from samples collected at approximately monthly intervals between January 1984 and December 1986. The prominent, narrow hyaline zone on otoliths was shown to be formed annually and thus valid for ageing these fish. An examination of the otoliths of 4711 fish indicated that 69.2 and 26.8% of the fish caught belonged to the 0 + and I + age classes, respectively. While the vast majority of the remaining fish represented the II + age class, a few III + and IV + and one V + fish were also recorded. Growth was seasonal, being greatest in spring and autumn and effectively ceasing in winter. Females began to grow faster than males during their first autumn of life. The respective mean lengths of males and females were 70 and 75 mm at the end of the first year and 90 and 100 mm at the end of the second year. The largest fish caught was a III + female measuring 163 mm and weighing 32.0 g. The respective von Bertalanffy growth curve parameters for L, K and t₀ were 109, 0.758 and - 0.338 for males, and 124, 0.762 and - 0.223 for females. Although the diet of G. occidentalis was always dominated by small terrestrial fauna, and particularly insects, conspicuous seasonal differences were found between the more important of the other components. Data on body size, growth and diet of G. occidentalis are compared with those recorded for other galaxiids.     

Coarse root biomass for eucalypt plantations in Tasmania,Australia: sources of variation and methods for assessment

This study develops a feasible method for evaluating coarse root biomass (roots >2 mm diameter) of well established plantations of eucalypts and then examines coarse root biomass variability across tree age and size, fertilization treatment, species and site for Eucalyptus globulus and E. nitens in Tasmania, Australia. The most efficient sampling protocol consisted of rootball excavation and soil coring for bulk coarse roots, which when compared with total tree excavation estimated total coarse root biomass contained inside the sampled area to within 10%. Across all treatments, an average of 76% of the coarse root biomass was located within the rootball. The majority (>65%) of the coarse roots outside the rootball were located in the surface 20 cm of soil. When size class distribution was examined, 75% of coarse root biomass was found to occur in the larger (20+ mm) diameter size class, a size class that displayed considerable spatial heterogeneity. At the stand level, coarse root biomass ranged from 2.18 to 7.38 kg m ^-2 depending primarily on tree size but also on fertilization treatment, species and site. It is estimated that allocation to coarse root biomass production was around 0.2 kg m ^-2 year ^-1 (around 6% of estimated NPP) for the E. nitens stands examined in this study and around 1 kg m ^-2 year ^-1 (around 20% of estimated NPP) for the E. globulus stand examined. Robust relationships using above-ground parameters could be used to predict coarse root biomass regardless of fertilization or site, but species changed the relationship.     

Rehabilitation of Swamp Paperbark (<Emphasis Type="Italic">Melaleuca ericifolia</Emphasis>) wetlands in south-eastern Australia: effects of hydrology,microtopography, plant age and planting technique on the success of community-based revegetation trials

Wetlands dominated by Swamp Paperbarks (Melaleuca spp., Myrtaceae) are common in coastal regions across Australia. Many of these wetlands have been filled in for coastal development or otherwise degraded as a consequence of altered water regimes and increased salinity. Substantial resources, often involving community groups, are now being allocated to revegetating the remaining wetland sites, yet only rarely is the effectiveness of the rehabilitation strategies or on-ground procedures robustly assessed. As part of a larger project investigating the condition and rehabilitation of brackish-water wetlands of the Gippsland Lakes, we overlaid a scientifically informed experimental design on a set of community-based planting trials to test the effects of water depth, microtopography, plant age and planting method on the survival and growth of seedlings of Melaleuca ericifolia Sm. in Dowd Morass, a degraded, Ramsar-listed wetland in south-eastern Australia. Although previous laboratory and greenhouse studies have shown M. ericifolia seedlings to be salt tolerant, the strongly interactive effects of waterlogging and salinity resulted in high seedling mortality (>90%) in the field-based revegetation trials. Seedlings survived best if planted on naturally raised hummocks vegetated with Paspalum distichum L. (Gramineae), but their height was reduced compared with seedlings planted in shallowly flooded environments. Age of plants and depth of water were important factors in the survival and growth of M. ericifolia seedlings, whereas planting method seemed to have little effect on survival. Improved testing of revegetation methods and reporting of success or otherwise of revegetation trials will improve the effectiveness and accountability of projects aiming to rehabilitate degraded coastal wetlands.     

Ontogenetic habitat shifts by Galaxias gracilis (Galaxiidae) between the littoral and limnetic zones of Lake Kanono, New Zealand

Synopsis Diel and spatial differences in distribution were determined for the larvae, juveniles, and adults of Galaxias gracilis (Galaxiidae) in a New Zealand dune lake during summer months. Larvae (mostly 10–25 mm TL) and juveniles (25–40 mm TL) inhabited shallow (0–3 m) waters of the limnetic zone and fed predominantly on two limnetic zooplankton species; Bosmina meridionalis and a calanoid copepod. At about 40 mm TL, fish moved from the limnetic to the littoral zone and expanded dietary breadth from two to over seven main prey species, including five species of littoral invertebrates. After reaching a size of about 60 mm TL, most fish moved back offshore to the deeper waters (5–15 m) of the limnetic zone during the day, moving back to the littoral zone at night to feed on invertebrates. The selection of different intra-lacustrine habitats by the various size groups of G. gracilis, and the movements between them, are interpreted as adaptive responses to the interaction between ontogenetic changes in feeding requirements and predation risk.