Population genetics of the Antarctic heteronemertean Parbolasia corrugatus from the South Orkney Islands

An allozyme survey, using starch-gel electrophoresis, was carried out on eight populations of the Antarctic nemertean worm Parborlasia corrugatus (McIntosh, 1876) collected from locations around the South Orkney Islands, Antarctica. These populations were separated by distances in the order of tens of kilometres. Genetic variation was estimated over 22 enzyme loci for all populations examined, giving an observed heterozygosity of 0.142. This was much lower than the expected heterozygosity (H _e  = 0.201), and it was found that there was a significant deficiency of het‐erozygotes across four enzyme loci ( p ≤ 0.01). A more detailed examination of this deficiency of heterozygotes was undertaken for the six populations and six variable enzyme loci for which the most complete data sets existed. A significant deficiency of heterozygotes was found at the enzyme locus Odh-1 for four of the six populations examined ( p ≤ 0.01). Mean F _is (0.240) indicated a significant ( p ≤ 0.01) within-population component of the heterozygote deficiency estimated for the six populations sampled, and this was mainly due to the␣Ap-1, Odh-1 and Pgm-1 loci. The mean F _st value (0.036) was also significant ( p ≤ 0.01), indicating a degree of genetic differentiation between populations. The observed levels of genetic differentiation between populations of P. corrugatus and the significant heterozygote deficiencies were unexpected, because this species has been reported to have a long-lived planktotrophic larva. It is hypothesised that recruitment of P. corrugatus in the South Orkney Islands originates from genetically distinct populations located in the Weddell Sea and to the west of the Antarctic Peninsula. Shifts in the relative position of the Weddell Sea Front, Weddell–Scotia Confluence and Scotia Front, relative to the South Orkney Islands, provide a mechanism for variation in the origin of recruits over time. Received: 24 July 1997 / Accepted: 31 October 1997     

Population structure in the sexually reproducing sea anemone Oulactis muscosa

The intertidal sea anemone Oulactis muscosa (Drayton) is dioecious and most individuals are sexually mature throughout the year. Biochemical genetic evidence was used to determine the genetic structure of populations and to infer the relative contributions of sexual and asexual reproduction to recruitment. Data were collected for six enzyme-encoding loci from local populations spread along 735 km of the south east coast of Australia. The genetic structure of each of the nine local populations studied was consistent with recruitment by sexually produced individuals. In almost all cases, the observed single-locus genotypic frequencies closely matched those expected for hardy-Weinberg equilibria, however, consistent deficits of heterozygotes were detected for all loci. No apparent subdivision of the population was detected within the sampling area. Low levels of genetic differentiation were found between local populations and standardised variance (F _ST ) values were similar to those for other species with widespread planktonic dispersal of larvae.Contribution No. 60 from the Ecology and Genetics Group of the University of Wollongong     

Genetic differentiation among populations of a broadcast spawning soft coral, Sinularia flexibilis, on the Great Barrier Reef

The genetic structure of 12 reef populations of the soft coral Sinularia flexibilis (Octocorallia, Alcyoniidae) was studied along the Great Barrier Reef (GBR) at a maximum separation of 1,300 km to investigate the relative importance of sexual and asexual reproduction, genetic differentiation and gene flow among these populations. S. flexibilis is a widely distributed Indo-Pacific species and a gamete broadcaster that can form large aggregations of colonies on near-shore reefs of the GBR. Up to 60 individuals per reef were collected at a minimum sampling scale of 5 m at two sites per reef, from December 1998 to February 2000. Electrophoretic analyses of nine polymorphic allozymes indicated that genotypic frequencies in most populations and loci did not differ significantly from those expected from Hardy–Weinberg predictions. Analysis of multi-locus genotypes indicated a high number of unique genotypes (N _go) relative to the number of individuals sampled (N) in each reef population (range of 0.69–0.95). The maximum number of individuals likely to have been produced sexually (N*) was similar to the number of individuals sampled (i.e. N*:N ˜ 1), suggesting that even repeated genotypes may have been produced sexually. These results demonstrated a dominant role of sexual reproduction in these populations at the scale sampled. Significant genetic differentiation between some populations indicated that gene flow is restricted between some reefs (F _ST=0.026, 95% CI= 0.011 − 0.045) and even between sites within reefs (F _ST=0.041, 95% CI=0.027 − 0.055). Nevertheless, there was no relationship between geographic separation and genetic differentiation. Analyses comparing groups of populations showed no significant differentiation on a north-south gradient in the GBR. The pattern in the number of significant differences in gene frequencies in pairwise population comparisons, however, suggested that gene flow may be more restricted among inner-shelf reef populations near to the coast than among mid/outer-shelf populations further from the coast. Received: 10 July 2000 / Accepted: 5 October 2000     

Genetic variation and clonal structure in the scleractinian coral Pocillopora damicornis in the Ryukyu Archipelago, southern Japan

Samples of the scleractinian coral Pocillopora damicornis were collected from six sites located around four islands in the Ryukyu Archipelago, southern Japan, and subjected to allozyme electrophoresis. Seven polymorphic loci were examined for their allelic patterns. The ratio of observed to expected genotypic diversity (0.30 < G _o :G _e  < 0.64), the ratio of the observed number of genotypes to the number of individuals (0.47 < N _g :N _i  < 0.75), and deviations from Hardy–Weinberg equilibrium indicated that asexual reproduction plays a major role in the maintenance of established populations. However, populations were not completely dominated by a single or a few clones, and most clones were represented by only a few individual samples. The high frequency of typhoons in the region suggests that, in P. damicornis, fragmentation caused through occasional exposure to powerful waves is a major mode of asexual reproduction, but asexual production of planulae may also be contributing to the maintenance of populations. A significant genetic differentiation (F ST) was found between the six populations examined (0.027 < F ST < 0.092, average F ST = 0.056). The moderate gene flow is discussed according to characteristics of the larval stage of the species, and to circulation patterns in the region. Received: 7 August 1998 / Accepted: 18 May 1999     

Coexistence of nine anemonefish species: differential host and habitat utilization, size and recruitment

The region of Madang, Papua New Guinea, has the highest reported species diversity of both anemonefishes (nine species) and their host anemones (ten species). To determine which factors may allow so many anemonefish species to coexist at this location, we studied their patterns of distribution, abundance, and recruitment. Population surveys at three replicate reef sites within four zones situated at varying distances from the mainland (nearshore, mid-lagoon, outer barrier, and offshore) indicated that each species of host anemone and anemonefish lived within a particular range of zones. Each species of anemonefish lived primarily with one species of host. Anemonefish species that lived with the same host species usually had different distribution patterns among zones (e.g., Amphiprion percula occupied Heteractis magnifica in nearshore zones, while A. perideraion occupied H. magnifica in offshore zones). Monitoring of natural populations showed that there were few changes (losses or recruitment) in the number or species of fishes associated with each individual anemone over periods ranging from 3 to 9 months. Recruitment was monitored on anemones with and without residents (resident fishes were removed) within each of three zones (nearshore, mid-lagoon, outer barrier). Significantly more anemonefishes recruited to anemones without resident fishes than to anemones with resident fishes. Each anemonefish species recruited to particular host species and zones. The distribution and abundance of the recruits of each fish species among zones were positively correlated with the distribution and abundance of resident fishes in the benthic habitat. This suggests that the spatial patterns of recruitment among zones strongly determined the distribution and abundance patterns of the benthic populations, and they were not the result of post-recruitment mortality or movement. Coexistence of the nine anemonefish species on the limited anemone resource was considered possible because of niche differentiation (i.e., differences in host and habitat utilization among zones), and the ability of two small species (i.e., Amphiprion sandaracinos and A. leucokranos) to cohabit individual anemones with other anemonefish species. Received: 29 July 1999 / Accepted: 1 September 2000     

Feeding and predator-avoidance by the rose anemone Urticina piscivora

We investigated the influence of feeding rate on the behavior of the rose anemone Urticina piscivora. We predicted that anemones would travel less and be less willing to detach from the substrate in response to contact with a predator (Dermasterias imbricata) as feeding rate was experimentally increased. As predicted, anemones receiving 0 mussels (Mytilustrossulus) daily moved significantly more than those receiving either 1 or 2 mussels daily. Anemones receiving 0 mussels daily also detached significantly quicker in response to predator contact compared to the 1 mussel per day group, which in turn detached significantly quicker than did the 2 mussels per day group. A field test of the same prediction gave mixed results. We also examined whether anemones could detect feeding rates of neighbors. Movement rates of anemones receiving 1 mussel daily when neighbors received 0 mussels daily were compared with those when neighbors received 2 mussels daily. We predicted that if the subjects could detect feeding rates of neighbors, they should move less when neighbors received less food than themselves (since their position is relatively good) than when neighbors received more food. The results support this interpretation. Received: 21 August 1996 / Accepted: 22 October 1996     

Genetic structure of populations of two species of Chthamalus (Crustacea: Cirripedia) in the north-east Atlantic and Mediterranean

Protein electrophoresis on starch gels was used to investigate population genetic structure of the barnacles Chthamalus montagui Southward and C. stellatus (Poli) over their north-east Atlantic and Mediterranean ranges. In each species, a single locus exhibited marked differentiation of allele frequencies between Atlantic and Mediterranean localities; in C. stellatus, genetic differentiation between the two basins had not previously been noted. In both species, mean heterozygosity per locus appeared higher in the Mediterranean samples than in the Atlantic, and Mediterranean populations had more alleles at the loci studied. Possible explanations for the differentiation between the Atlantic and the Mediterranean populations are discussed. Received: 30 May 1996 / Accepted: 17 September 1996     

A comparative analysis of the photobiology of Zooxanthellae and Zoochlorellae symbiotic with the temperate clonal anemone Anthopleura elegantissima (Brandt) I. Effect of temperature

Throughout its geographic range, the temperate-zone anemone Anthopleura elegantissima is the host of one or both of two distinctively different symbiotic microalgae: a dinoflagellate Symbiodinium (zooxanthellae, ZX) and a chlorophyte (zoochlorellae, ZC). Given the broad vertical intertidal and latitudinal range of this anemone, we investigated the role of temperature in determining whether A. elegantissima supports one algal symbiont over the other and whether temperature regulates the observed distributions of natural populations of ZX and ZC. Temperature appears to be a key factor in regulating both the photophysiology and metabolism of this algal–cnidarian association. In anemones containing ZX, neither algal densities nor chlorophyll content varied with temperature (6–24 °C); in contrast, anemones with ZC displayed reduced densities and chlorophyll content at the highest temperature treatment (24 °C). Both ZX and ZC photosynthetic rates were directly related to temperature, as were anemone respiration rates. The higher photosynthetic rates, maintenance of a stable algal density and chlorophyll content, and higher potential contribution of algal carbon toward animal respiration (CZAR) suggest that the ZX are the more viable symbiont as temperature increases, but we suggest alternative reasons why ZC are preserved in this symbiotic association. Elevated temperatures reduce ZC densities and chlorophyll, suggesting that higher temperatures affect this relationship in a negative fashion, presumably due to a higher cost of maintaining ZC by the association; alternatively, these costs may be affiliated with the deterioration of the ZC themselves. These results suggest that temperature may be one of the most significant environmental parameters that sets the intertidal microhabitat and latitudinal distribution patterns of the two algal taxa observed in the field. Received: 2 November 1998 / Accepted: 25 October 2000     

Allozyme electrophoresis indicates high gene flow between populations of Holothuria (Microthele) nobilis (Holothuroidea: Aspidochirotida) on the Great Barrier Reef

 Genetic variation in 15 Holothuria (Microthele) nobilis (Selenka, 1867) populations on the Great Barrier Reef was studied at seven polymorphic allozyme loci. Although populations were separated by distances up to 1300 km, there were no apparent restrictions to gene flow (F _ST values were not significantly different from 0) and the maximum Nei's unbiased genetic distance was 0.003. Populations were in Hardy–Weinberg equilibrium at all loci. The estimated maximum sexual input [this is the ratio of the number of sexually produced individuals (N*) to the sample size (N _i )] and the minimum sexual input [this is the ratio of the number of genotypes (N _go ) over the sample size (N _i )] were used as estimators for the amount of asexual reproduction. Both parameters suggested that H. nobilis reproduces solely by sexual means (N*:N _i : = 1; N _go :N _i  = 0.74 to 1). The allozyme data indicated high gene flow between populations, but the possibility that allozyme frequencies may not be at equilibrium means that it was not possible to distinguish whether the patterns reflect present-day dispersal or dispersal that occurred in the past. Received: 27 March 2000 / Accepted: 29 June 2000     

Genetic structure and allozyme variation of sea bass (Dicentrarchus labrax and D. punctatus) in the Mediterranean Sea

This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F _ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at “neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species in Egypt; thus gene flow was not indicated between species. Received: 24 October 1996 / Accepted: 27 November 1996     

Reproductive strategies of Mycalecontarenii (Porifera: Demospongiae)

The sexual and asexual phases of the reproductive cycle of the sponge Mycalecontarenii (Martens, 1824) were studied from samples collected over a period of 2 years (June 1994 to May 1996) in a Mediterranean coastal basin (Porto Cesareo, southwestern Apulia). The species is viviparous; year round it shows a discontinuous oocyte production. No males were found, possibly owing to the very short period of spermatogenesis. M.␣contarenii produces asexual buds during autumn and winter, and this process seems to be related to changes in water temperature. Even though, at present, we cannot evaluate the incidence of larval recruitment, we postulate that asexual reproduction in M.contarenii plays a crucial role in maintaining the sponge population. Received: 8 July 1997 / Accepted: 5 November 1997     

A comparative analysis of the photobiology of zooxanthellae and zoochlorellae symbiotic with the temperate clonal anemone <Emphasis Type="Italic">Anthopleura elegantissima</Emphasis> (Brandt). III. Seasonal effects of natural light and temperature on photosynthesis and respiration

The sea anemone Anthopleura elegantissima hosts two phylogenetically different symbiotic microalgae, a dinoflagellate Symbiodinium (zooxanthellae, ZX) and a chlorophyte (zoochlorellae, ZC). The photosynthetic productivity (P), respiration (R), and contribution of algal carbon translocated to the host (CZAR) in response to a year’s seasonal ambient changes of natural light and temperature are documented for both ZX- and ZC-bearing anemones. Light and temperature both affect photosynthesis, respiration, and CZAR, as well as various algal parameters; while there are evident seasonal differences, for the most part the relative effects on P, R, and CZAR by the two environmental variables cannot be determined. Net photosynthesis (P_n) of both ZX and ZC was significantly higher during spring and summer. During these seasons, the P_n of ZX was always greater than that of ZC. Regardless of algal symbiont, anemone respiration (R) was significantly higher during the spring and summer. The annual net carbon fixation rate of anemones with ZX and ZC was 325 and 276 mg C anemone⁻¹ year⁻¹, respectively, which translates to annual net community productivity rates of 92 and 60 g C m⁻¹ year⁻¹ for anemones with ZX or ZC, respectively. CZAR did not show a clear relationship with season; however the CZAR for ZX was always significantly greater than for ZC. Lower ZX growth rates, coupled with higher photosynthetic rates and higher CZAR estimates, compared to ZC, suggest that if A. elegantissima is simply carbon limited, ZX-bearing anemones should be the dominant symbiont in the field. However ZC-bearing anemones persist in low light and reduced temperature microhabitats, therefore more than the translocation of carbon from ZC must be involved. Given that global climate change will increase water temperatures, the potential for latitudinal range shifts of both ZC and ZX (S. californium and muscatinei) might be used as biological indicators of thermal shifts in the littoral zone of the Pacific Northwest.     

Population structure and genetic variation in two tropical sea anemones (Cnidaria,Actinidae) with different reproductive strategies

Genetic variation and population structure of two tropical sea anemones, Bunodosoma caissarum Correa and Actinia bermudensis McMurrich were related to their different dispersal capabilities and reproductive modes. B. caissarum reproduces sexually and has a long-lived planktotrophic larva; A. bermudensis can reproduce both sexually and asexually, supposedly with short-range dispersal. Both species were sampled along 1150 km of Brazilian coastline between 1990 and 1991 and analyzed by horizontal starch gel electrophoresis for 16 enzyme loci in B. caissarum and 19 in A. bermudensis. B. caissarum had higher levels of heterozygosity (H=0.35) and lower levels of population structuring (F _ST=0.042) than A. bermudensis (H=0.17; F _ST=0.262). At one locality large genetic differences between two sympatric colour morphs of A. bermudensis provide evidence of possible cryptic speciation. Overall levels of genetic variation and heterozygosity in the two species are compatible with their known modes of reproduction.     

Population genetic structure in brooding sea anemones (Epiactis spp.) with contrasting reproductive modes

Effects of dispersal and mating systems on the genetic structure of populations were evaluated by comparing five sea anemones: four Epiactis species that brood their offspring to the juvenile stage and one Anthopleura species that broadcasts gametes and has pelagic, planktotrophic larvae. The anemones were sampled at sites ranging from British Columbia to southern California between 1988 and 1992 and were analyzed by enzyme electrophoresis and by multilocus DNA-fingerprinting. Results were only partially consistent with expectations. While all four brooding species had lower observed heterozygosities than the broadcasting species, not all brooding species had greater population subdivision than the broadcasting species. The self-fertile E. prolifera had the expected evidence of intense local inbreeding ( f = 0.955); unexpectedly, the cross-fertile E. lisbethae and E. ritteri also had similar departures from random mating ( f = 0.957 and 0.831, respectively) probably due to biparental inbreeding among near neighbors in small, highly subdivided populations. Received: 24 May 1996 / Accepted: 12 July 1996     

Genetic relationships within and between clonal and solitary forms of the sea anemone Anthopleura elegantissima revisited: evidence for the existence of two species

Along the temperate Pacific coast of North America, the actiniarian sea anemone Anthopleura elegantissima exhibits two discrete life-history phenotypes. Although both forms sexually produce planula larvae, the clonal morph can also asexually propagate by fission, whereas the solitary morph does not. Whether the two forms constitute one or two species has long been contested. Hand originally designated the two forms as conspecifics, whereas Francis – on the basis of differences in microhabitat, biogeographic range and phenotypic frequencies – argued that the two forms constituted a sibling-species pair. From the results of an electrophoretic survey in which they pooled allelic frequencies across several geographic locations, Smith and Potts subsequently argued that the two forms were not genetically differentiated, and therefore represented a single species. We re-examined the relationship between the forms electrophoretically, substantially extending the geographic range and doubling the sample sizes beyond those used by Smith and Potts, and not pooling allelic frequencies in our analyses. Our analysis of patterns of genetic variation at ten highly polymorphic allozyme loci shows that although no fixed genetic differences distinguish the two forms, there are significant differences in allele frequencies between clonal and solitary A.␣elegantissima at every site we sampled throughout their range of sympatry (over 1000 km); within each form, however, there is little detectable genetic differentiation among populations. We therefore conclude that the two forms represent recently reproductively isolated taxa, and propose that the clonal form retain the binomial A. elegantissima (Brandt, 1835), whereas the solitary form be described and named a new species, Anthopleura sp. Received: 28 August 1996 / Accepted: 25 September 1996     

Asexual viviparity and population genetics of Actinia tenebrosa

The intertidal anemone Actinia tenebrosa is viviparous. An electrophoretic study of 3 polymorphic enzymes in Western Australian populations has confirmed genetic identity of adults and their brood young, indicating asexual reproduction. The population effects of this clonal reproduction are seen as linkage disequilibrium and departures from Hardy-Weinberg equilibrium within populations, and large differences between populations. The data also suggest occasional sexual reproduction, and the likelihood of a mixture of reproductive modes in this species.     

Evidence of amictic reproduction in the brittle-star Ophiomyxa brevirima

Ophiomyxa brevirima is a direct-developing species of brittle-star found around the coast of New Zealand. The mode of reproduction of this ophiuroid was studied using isozyme electrophoresis of mother and brooded offspring. Multi-locus assessment of the genotypes of 35 adult females and their brooded offspring was undertaken. A minimum of 45% of broods assessed showed evidence of amictic reproduction, with all offspring in these broods possessing genotypes that were identical to the genotype of their heterozygous mother. In most other broods there was evidence of segregation. These observations are interpreted as evidence of both sexual and asexual reproduction in this ophiuroid species. Received: 19 November 1996 / Accepted: 28 January 1997     

Mortality is associated with social rank in the clown anemonefish (<Emphasis Type="Italic">Amphiprion percula</Emphasis>)

Elucidating the causes of post-recruitment mortality is a vital step toward understanding the population dynamics of coral reef fishes. Predation is often considered to be the primary proximate cause of mortality. It has, however, proven difficult to discern the relative contributions of predation and other processes, such as competition for food, shelter, or mates, to patterns of mortality. To determine which other processes might be important drivers of mortality patterns, factors related to mortality in the clown anemonefish Amphiprion percula (Lacepède, 1802) were examined. Patterns of mortality will not be driven by predation in A. percula, because these fish are well protected from predators by their close association with sea anemones. Mortality rates were based on the disappearance of known individuals from a population of 201, in 57 groups, during a 1-year field study (in 1997), in Madang Lagoon, Papua New Guinea. Mortality rate of A. percula was low (14% per annum) compared to other coral reef fish, probably due to the protection from predators afforded by the anemone. Six factors (reef, depth, anemone diameter, number of individuals, density, and standard length) showed no association with the probability of mortality (P>0.05). Rank was the only factor associated with the probability of mortality (P<0.03); low-rank individuals (ranks 4–6) suffered a higher mortality rate than high-rank individuals (ranks 1–3) (P<0.01). The most likely explanation for this pattern was that competition for rank, amongst individuals within an anemone, resulted in some individuals evicting their subordinates. Individuals probably competed for rank because it conferred access to reproduction, and not because it conferred access to food or shelter. Such competition for reproduction will be intense whenever some individuals obtain a greater share of reproduction than others do, and it may be an important process influencing the dynamics of coral reef fish populations.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Communicated by J.P. Grassle, New Brunswick     

The effects of symbiotic state on heterotrophic feeding in the temperate sea anemone <Emphasis Type="Italic">Anthopleura elegantissima</Emphasis>

The temperate sea anemone Anthopleura elegantissima is facultatively symbiotic with unicellular algae. Symbiotic A. elegantissima can supplement heterotrophic feeding with excess photosynthate from their algal partners, while asymbiotic individuals must rely solely on heterotrophy. A. elegantissima individuals were collected from Swirl Rocks, Washington (48°25′6″ N, 122°50′58″ W) in July 2010, and prey capture and feeding characteristics were measured to determine whether asymbiotic individuals are more efficient predators. Feeding abilities were then measured again after a 3-week exposure to full sunlight or shaded conditions. Freshly collected asymbiotic anemones had larger nematocysts, but symbiotic individuals showed greater nematocyte sensitivity. Sunlight enhanced digestion and reduced cnida density in all anemones regardless of symbiotic state. Results suggest that the phototropic potential of A. elegantissima, as influenced by symbiotic condition, has little effect on heterotrophic capacity. The anemones appear to maximize heterotrophic energy input independent of the presence or identity of their algal symbionts.     

Parthenogenetic reproduction of Diaphanosoma celebensis (Crustacea: Cladocera): influence of salinity on feeding, survival, growth and neonate production

 Effect of salinity on the feeding rate and parthenogenetic reproduction of asexual females of the cladoceran Diaphanosoma celebensis Stingelin was studied. Short-term (10 h) grazing experiments were conducted using Isochrysis galbana as feed at 5, 17, 25 and 30 psu salinity. Gut pigment concentration showed a significantly higher rate of feeding at lower salinities. Survival, growth, maturity attainment and neonate production of asexual females reared in the above four test salinities indicated preference for lower salinities (5 and 17 psu). The mean size of adult females decreased from 909 to 593 μm, mean life span from 24 to 5 d, mean neonate production from 12 to 2 and mean size of neonates from 434 to 400 μm as the salinity increased from 5 to 30 psu. Salinity variations also affected the size and age of primiparous females. Resting egg formation and sexual reproduction did not occur at the tested salinities. The results indicate that D. celebensis is adapted to low saline, estuarine environments. Received: 14 January 2000 / Accepted: 24 March 2000