MOLECULAR GENETIC EVIDENCE FOR PARALLEL LIFE-HISTORY EVOLUTION WITHIN A PACIFIC SALMON (SOCKEYE SALMON AND KOKANEE,ONCORHYNCHUS NERKA)

The Pacific salmon Oncorhynchus nerka typically occurs as a sea-run form (sockeye salmon) or may reside permanently in lakes (kokanee) thoughout its native North Pacific. We tested whether such geographically extensive ecotypic variation resulted from parallel evolutionary divergence thoughout the North Pacific or whether the two forms are monophyletic groups by examining allelic variation between sockeye salmon and kokanee at two minisatellite DNA repeat loci and in mitochondrial DNA (mtDNA) Bgl II restriction sites. Our examination of over 750 fish from 24 populations, ranging from Kamchatka to the Columbia River, identified two major genetic groups of North Pacific O. nerka: a “northwestern” group consisting of fish from Kamchatka, western Alaska, and northwestern British Columbia, and a “southern” group consisting of sockeye salmon and kokanee populations from the Fraser and Columbia River systems. Maximum-likelihood analysis accompanied by bootstrapping provided strong support for these two genetic groups of O. nerka; the populations did not cluster by migratory form, but genetic affinities were organized more strongly by geographic proximity. The two major genetic groups resolved in our study probably stem from historical isolation and dispersal of O. nerka from two major Wisconsinan glacial refugia in the North Pacific. There were significant minisatellite DNA allele frequency differences between sockeye salmon and kokanee populations from different parts of the same watershed, between populations spawning in different tributaries of the same lake, and also between sympatric populations spawning in the same stream at the same time. MtDNA Bgl II restriction site variation was significant between sockeye salmon and kokanee spawning in different parts of the same major watershed but not between forms spawning in closer degrees of reproductive sympatry. Patterns of genetic affinity and allele sharing suggested that kokanee have arisen from sea-run sockeye salmon several times independently in the North Pacific. We conclude that sockeye salmon and kokanee are para- and polyphyletic, respectively, and that the present geographic distribution of the ecotypes results from parallel evolutionary origins of kokanee from sockeye (divergences between them) thoughout the North Pacific.     

Reproductive Cycle and Developmental Processes During Embryogenesis of Clavularia hamra (Cnidaria,Octocorallia)

Clavularia hamra Gohar, 1948 is a common octocoral on the reefs of the Gulf of Eilat (northern Red Sea). Reproductive biology of C. hamra was studied for two years. Direct observations of spawning were conducted in situ and in aquaria. Cleavage of eggs and further embryo metamorphosis into mature planulae were examined by scanning electron microscopy and histological sections. Clavularia hamra is dioecious. Young oocytes appear annually in September, gradually grow in size and attain maturity within 11 months. The main spawning event of the population is highly synchronized, occurring on a single night each year between the last quarter and the new moon in mid summer. The released orange eggs are held together by mucus and remain attached amongst the polyps on the outside of the female colonies. Twelve hours after spawning, the young embryos have blastomeres of equal size with numerous microvilli on their external surface. Due to unequal cleavage, bizarre embryos are also formed. By 48 h a blastopore is visible, indicating that a gastrula is developing. Eight days after spawning mature planulae are observed. The external mode of embryo development on the surface of the parent colony reduces dispersal of the planulae. However, this reproductive feature enhances formation of locally dense populations of C. hamra, with distinct habitat preferences.     

Spatial variation in the effects of size and age on reproductive dynamics of common coral trout Plectropomus leopardus

The effects of size and age on reproductive dynamics of common coral trout Plectropomus leopardus populations were compared between coral reefs open or closed (no‐take marine reserves) to fishing and among four geographic regions of the Great Barrier Reef (GBR), Australia. The specific reproductive metrics investigated were the sex ratio, the proportion of vitellogenic females and the spawning fraction of local populations. Sex ratios became increasingly male biased with length and age, as expected for a protogyne, but were more male biased in southern regions of the GBR (Mackay and Storm Cay) than in northern regions (Lizard Island and Townsville) across all lengths and ages. The proportion of vitellogenic females also increased with length and age. Female P. leopardus were capable of daily spawning during the spawning season, but on average spawned every 4·3 days. Mature females spawned most frequently on Townsville reserve reefs (every 2·3 days) and Lizard Island fished reefs (every 3·2 days). Females on Mackay reefs open to fishing showed no evidence of spawning over 4 years of sampling, while females on reserve reefs spawned only once every 2–3 months. No effect of length on spawning frequency was detected. Spawning frequency increased with age on Lizard Island fished reefs, declined with age on Storm Cay fished reefs, and declined with age on reserve reefs in all regions. It is hypothesized that the variation in P. leopardus sex ratios and spawning frequency among GBR regions is primarily driven by water temperature, while no‐take management zones influence spawning frequency depending on the region in which the reserve is located. Male bias and lack of spawning activity on southern GBR, where densities of adult P. leopardus are highest, suggest that recruits may be supplied from central or northern GBR. Significant regional variation in reproductive traits suggests that a regional approach to management of P. leopardus is appropriate and highlights the need for considering spatial variation in reproduction where reserves are used as fishery or conservation management tools.     

Spawning behavior ofChaetodon multicinctus (Chaetodontidae); pairs and intruders

Synopsis Spawning by the banded butterflyfish,Chaetodon multicinctus (Chaetodontidae) was observed on coral reefs off Kona, Hawaii. These fish occurred in male-female pairs during normal daytime activities, a behavior which is typical for the family. Courtship is also a paired male-female activity. During spawning, however, other individuals (males?) may intrude on the spawning pair. Spawning typically takes place at least a meter or two above the bottom. The spawning position consists of the male below and behind the female with his snout against the female's ventral flank or anal fin area. Intruding individuals may join in when the pair is in position and about to spawn. Intruders line-up against the male in the same position as he is against his female. Underwater photographs are included to illustrate these behaviors.     

Population genetics of reef coral endosymbionts (Symbiodinium,Dinophyceae)

Symbiodinium is a diverse genus of unicellular dinoflagellate symbionts associating with various marine protists and invertebrates. Although the broadscale diversity and phylogenetics of the Symbiodinium complex is well established, there have been surprisingly few data on fine‐scale population structure and biogeography of these dinoflagellates. Yet population‐level processes contribute strongly to the biology of Symbiodinium, including how anthropogenic‐driven global climate change impacts these symbionts and their host associations. Here, we present a synthesis of population‐level characteristics for Symbiodinium, with an emphasis on how phylogenetic affinities, dynamics within and among host individuals, and a propensity towards clonality shape patterns on and across reefs. Major inferences include the following: (i) Symbiodinium populations within individual hosts are comprised mainly of cells belonging to a single or few genetic clones. (ii) Symbiont populations exhibit a mixed mode of reproduction, wherein at least one sexual recombination event occurs in the genealogy between most genotypes, but clonal propagation predominates overall. (iii) Mutualistic Symbiodinium do not perpetually persist outside their hosts, instead undergoing turnover and replacement via the continuous shedding of viable clonal cells from host individuals. (iv) Symbiont populations living in the same host, but on different reefs, are often genetically subdivided, suggesting low connectivity, adaptation to local conditions, or prolific asexual reproduction and low effective population sizes leading to disproportionate success within and among hosts. Overall, this synthesis forms a basis for future investigations of coral symbiosis ecology and evolution as well as delimitation of species boundaries in Symbiodinium and other eukaryotic microorganisms.     

Temporal constraints on the potential role of fry odors as cues of past reproductive success for spawning lake trout

Deciding where to reproduce is a major challenge for most animals. Many select habitats based upon cues of successful reproduction by conspecifics, such as the presence of offspring from past reproductive events. For example, some fishes select spawning habitat following odors released by juveniles whose rearing habitat overlaps with spawning habitat. However, juveniles may emigrate before adults begin to search for spawning habitat; hence, the efficacy of juvenile cues could be constrained by degradation or dissipation rates. In lake trout (Salvelinus namaycush), odors deposited by the previous year's offspring have been hypothesized to guide adults to spawning reefs. However, in most extant populations, lake trout fry emigrate from spawning reefs during the spring and adults spawn during the fall. Therefore, we postulated that the role of fry odors in guiding habitat selection might be constrained by the time between fry emigration and adult spawning. Time course chemical, physiological, and behavioral assays indicated that the odors deposited by fry likely degrade or dissipate before adults select spawning habitats. Furthermore, fry feces did not attract wild lake trout to constructed spawning reefs in Lake Huron. Taken together, our results indicate fry odors are unlikely to act as cues for lake trout searching for spawning reefs in populations whose juveniles emigrate before the spawning season, and underscore the importance of environmental constraints on social cues.     

Fifty million years of herbivory on coral reefs: fossils,fish and functional innovations

The evolution of ecological processes on coral reefs was examined based on Eocene fossil fishes from Monte Bolca, Italy and extant species from the Great Barrier Reef, Australia. Using ecologically relevant morphological metrics, we investigated the evolution of herbivory in surgeonfishes (Acanthuridae) and rabbitfishes (Siganidae). Eocene and Recent surgeonfishes showed remarkable similarities, with grazers, browsers and even specialized, long-snouted forms having Eocene analogues. These long-snouted Eocene species were probably pair-forming, crevice-feeding forms like their Recent counterparts. Although Eocene surgeonfishes likely played a critical role as herbivores during the origins of modern coral reefs, they lacked the novel morphologies seen in modern Acanthurus and Siganus (including eyes positioned high above their low-set mouths). Today, these forms dominate coral reefs in both abundance and species richness and are associated with feeding on shallow, exposed algal turfs. The radiation of these new forms, and their expansion into new habitats in the Oligocene–Miocene, reflects the second phase in the development of fish herbivory on coral reefs that is closely associated with the exploitation of highly productive short algal turfs.     

Spawning seasons of Rasbora tawarensis (Pisces: Cyprinidae) in Lake Laut Tawar,Aceh Province,Indonesia

Background  

Rasbora tawarensis is an endemic freshwater fish in Lake Laut Tawar, Aceh Province, Indonesia. Unfortunately, its status is regarded as critical endangered with populations decreasing in recent years. To date no information on the spawning activities of the fish are available. Therefore, this study provides a contribution to the knowledge on reproductive biology of R. tawarensis especially on spawning seasons as well as basic information for conservation of the species.     

Sound Production in Codoma ornata (Girard) (Cyprinidae)

Male Codoma ornata produce sounds associated with aggression and spawning activities during the breeding season. Females do not produce sounds. Males most often produced sounds associated with escalated displays of aggression, courtship and the spawning act. C. ornata spawn in crevices, but previously were reported to spawn as egg-clusterers in cavities. Structurally, sounds are low frequency, vary in duration according to context and are not harmonic. The mechanism of sound production is unknown.     

Genetic structure of giant clam (Tridacna maxima) populations from reefs in the Western Coral Sea

Allozyme variation at six polymorphic loci was examined in 10 populations of Tridacna maxima from reefs in the Western Coral Sea, to test whether patterns of relatedness previously reported for foraminiferan populations reflected a fundamental structuring of the fauna in the region. Genetic distances (Nei's D) among populations of T. maxima ranged from 0–0.065 and increased with increasing geographical separation. No significant differences in gene frequencies were observed among populations within two groups of reefs identified by cluster analysis: the Great Barrier Reef (GBR), and among the offshore reefs excluding Lihou and Osprey. Significant genetic differences among these groups and the outliers Lihou and Osprey were consistent with the greater geographical separation of populations between areas than within areas. There was no evidence of differentiation along a north-south axis as reported for the foraminiferan Marginopora vertebralis, nor did populations from offshore reefs on the Queensland Plateau form a well-defined group that was genetically distinct from the GBR. The patterns observed for M. vertebralis do not appear to reflect a fundamental structuring of biota in the region. The differences in the pattern of genetic variation for M. vertebralis as compared with those for T. maxima may be due to several differences in the biological characteristics of the two species. The time of breeding in particular may influence the extent to which the divergence of the East Australian Current restricts larval dispersal among reefs in the central Queensland Plateau.     

Recruitment constraints in Singapore's fluted giant clam (Tridacna squamosa) population—A dispersal model approach

Recruitment constraints on Singapore''s dwindling fluted giant clam, Tridacna squamosa, population were studied by modelling fertilisation, larval transport, and settlement using real-time hydrodynamic forcing combined with knowledge of spawning characteristics, larval development, behaviour, and settlement cues. Larval transport was simulated using a finite-volume advection-diffusion model coupled to a three-dimensional hydrodynamic model. Three recruitment constraint hypotheses were tested: 1) there is limited connectivity between Singapore''s reefs and other reefs in the region, 2) there is limited exchange within Singapore''s Southern Islands, and 3) there exist low-density constraints to fertilisation efficacy (component Allee effects). Results showed that connectivity among giant clam populations was primarily determined by residual hydrodynamic flows and spawning time, with greatest chances of successful settlement occurring when spawning and subsequent larval dispersal coincided with the period of lowest residual flow. Simulations suggested poor larval transport from reefs located along the Peninsular Malaysia to Singapore, probably due to strong surface currents between the Andaman Sea and South China Sea combined with a major land barrier disrupting larval movement among reefs. The model, however, predicted offshore coral reefs to the southeast of Singapore (Bintan and Batam) may represent a significant source of larvae. Larval exchange within Singapore''s Southern Islands varied substantially depending on the locations of source and sink reefs as well as spawning time; but all simulations resulted in low settler densities (2.1–68.6 settled individuals per 10,000 m²). Poor fertilisation rates predicted by the model indicate that the low density and scattered distribution of the remaining T. squamosa in Singapore are likely to significantly inhibit any natural recovery of local stocks.     

Natural spawning of a Hawaiian sea urchin,Tripneustes gratilla

Observations of natural spawning events are rare but critically important for the field of fertilization ecology. For broadcast spawners, knowing the natural behavior of spawning, including proximity of animals and the timing of spawning, is essential for informing spawning experiments and directing future study. Here we describe a natural spawning event that took place on the island of Maui in the winter of 2010. Groups of Tripnuestes gratilla were observed to spawn in the late afternoon shortly after a local high tide that was a lower high of a mixed, semidiurnal tide cycle. Urchins appeared to increase the probability of fertilization by ascending to the local high points of the reefs and spawning within groups of 2–5. Although the majority of the urchins that spawned were T. gratilla, two individuals of Echinothrix diadema were observed to spawn at the same time, raising questions about potential hybridization in the wild.     

Diel and lunar spawning periodicity of the hawkfish Paracirrhites forsteri (Cirrhitidae) on the reefs of Kuchierabu-jima Island, southern Japan

We observed spawning behavior of the hawkfish Paracirrhites forsteri on reefs of southern Japan. Spawning generally occurred after sunset, prior to the full and new moon with semi-lunar spawning peak periodicity. No egg predation was observed in spawning after sunset, and high tide often occurred at dusk in the lunar phases. Thus, diel timing and lunar synchronicity may increase larval survival. We found that the mating activity tended to start earlier in the day during early mating season than during mid-to-late mating season. The advantages of the earlier start of mating activity were also examined in relation to adult biology contexts.     

Genetic effects of habitat restoration in the Laurentian Great Lakes: an assessment of lake sturgeon origin and genetic diversity

Lake sturgeon (Acipenser fulvescens) have experienced significant habitat loss, resulting in reduced population sizes. Three artificial reefs were built in the Huron‐Erie corridor in the Great Lakes to replace lost spawning habitat. Genetic data were collected to determine the source and numbers of adult lake sturgeon spawning on the reefs and to determine if the founder effect resulted in reduced genetic diversity. DNA was extracted from larval tail clips and 12 microsatellite loci were amplified. Larval genotypes were then compared to 22 previously studied spawning lake sturgeon populations in the Great Lakes to determine the source of the parental population. The effective number of breeders (N_b) was calculated for each reef cohort. The larval genotypes were then compared to the source population to determine if there were any losses in genetic diversity that are indicative of the founder effect. The St. Clair and Detroit River adult populations were found to be the source parental population for the larvae collected on all three artificial reefs. There were large numbers of contributing adults relative to the number of sampled larvae. There was no significant difference between levels of genetic diversity in the source population and larval samples from the artificial reefs; however, there is some evidence for a genetic bottleneck in the reef populations likely due to the founder effect. Habitat restoration in the Huron‐Erie corridor is likely resulting in increased habitat for the large lake sturgeon population in the system and in maintenance of the population's genetic diversity.     

Spatial genetic features of eastern oysters (Crassostrea virginica Gmelin) in the Gulf of Mexico: northward movement of a secondary contact zone

The eastern oyster (Crassostrea virginica Gmelin) is an economically and ecologically valuable marine bivalve occurring in the Gulf of Mexico. This study builds upon previous research that identified two divergent populations of eastern oysters in the western Gulf of Mexico. Allelic and genotypic patterns from 11 microsatellite markers were used to assess genetic structure and migration between the previously described oyster populations in Texas. The main findings are as follows: (1) there are two distinct populations (F_ST = 0.392, P < 0.001) of oysters that overlap in the Corpus Christi/Aransas Bay estuarine complex in Texas, (2) the distribution of genotypes among individuals in the contact zone suggests limited hybridization between populations, (3) the variables of salinity, temperature, dissolved oxygen, turbidity and depth are not correlated with allele frequencies on reefs in the contact zone or when analyzed across Texas, and (4) there is little evidence of directional selection acting on the loci assayed here, although patterns at four markers suggested the influence of balancing selection based on outlier analyses. These results are consistent with long‐term historical isolation between populations, followed by secondary contact. Recent hydrological changes in the area of secondary contact may be promoting migration in areas that were previously inhospitable to eastern oysters, and observed differences in the timing of spawning may limit hybridization between populations. Comparison of these findings with the results of an earlier study of oysters in Texas suggests that the secondary contact zone has shifted approximately 27 km north, in as little as a 23‐year span.     

Mass spawning of corals on a high latitude coral reef

Evidence is presented that at least 60% of the 184 species of scleractinian corals found on reefs surrounding the Houtman Abrolhos Islands (Western Australia) participate in a late summer mass spawning. These populations are thus reproductively active, despite most species being at the extreme southern limit of their latitudinal range (28° 29°S). In the present study, coral mass spawning occurred in the same month on both temperate (Houtman-Abrolhos) and tropical (Ningaloo) reefs of Western Australia, despite more than two months difference in the timing of seasonal temperture minima between the two regions. This concurrence in the month of spawning suggests that temperature does not operate as a simple direct proximate cue for seasonal spawning synchrony in these populations. Seasonal variation in photoperiod may provide a similar and more reliable signal in the two regions, and thus might be more likely to synchronize the seasonal reproductive rhythms of these corals. Also there is overlap in the nights of mass spawning on the Houtman Abrolhos and tropical reefs of Western Australia, despite significant differences in tidal phase and amplitude between the two regions. This indicates that tidal cycle does not synchronize with the night(s) of spawning on these reefs. Spawning is more likely to be synchronised by lunar cycles. The co-occurrence of the mass spawning with spring tides in Houtman Abrolhos coral populations may be evidence of a genetic legacy inherited from northern, tropical ancestors. Micro-tidal regimes in the Houtman Abrolhos region may have exerted insufficient selective pressure to counteract this legacy.     

Population variation in spawning current speed selection in the blacktail shiner,Cyprinella venusta (Pisces: Cyprinidae)

Synopsis Many stream fishes lay demersal eggs. Some species simply scatter the eggs across the substrate, but many place the eggs in protected sites such as crevices (e.g., Cyprinidae:Cyprinella). Eggs laid in crevices may experience increased development times or lower embryo survival due to reduced water exchange rates compared to more open egg deposition sites. If so, the presence of an appreciable current near the crevice may be important for insuring water exchange. However, currents that are too strong may prevent complete insemination or prevent the eggs from adhering to the substratum before they are washed from the crevice. Thus, current speed preferences for spawning may be under strong stabilizing selection. Representatives of four populations of a crevice spawning stream fish (blacktail shiner,Cyprinella venusta), representing environments ranging from a swift stream to a lake, were studied in stream tanks to evaluate female spawning current use. The observed frequency of use of spawning currents was significantly different from random in all populations. Low current speeds were generally avoided, and a speed of ca. 30 cm sec^–1 was used most often. However, significant differences were observed among populations, and the variation correlated well with the apparent range of current speeds found in the four environments. Although other possible explanations cannot be dismissed, the results are consistent with the hypothesis that the populations have become adapted to their local current regimes.Authorship in order of seniority     

Gametogenesis, spawning and fecundity of Platygyra daedalea (Scleractinia) on equatorial reefs in Kenya

The reproductive ecology of the hermaphroditic broadcast spawning scleractinian reef coral Platygyra daedalea was studied on lagoonal reefs in Kenya. While single annual gametogenic cycles occurred in 84% of colonies, biannual gametogenic cycles were recorded in 16% of colonies and these patterns occurred in two morphotypes. In colonies with a single annual cycle, oogenesis occurred for 6–7 months from September to March and spermatogenesis for 5 months from November to March. In biannually spawning colonies, oogenic cycles overlapped for at least 2 months prior to gamete release. The major spawning period occurred in February and March, with minor spawning also occurring in August–October in biannually spawning colonies. Reproductive effort was lower during the minor winter compared to the major summer spawning, with fewer colonies reproducing (12.5–19.2%), not all mesenteries producing oocytes (32.5%) and less than half of the mesenteries with mature oocytes had associated spermaries (48.1%).     

Reproductive behavior of largemouth triplefin Ucla xenogrammus (Tripterygiidae) on reefs of Kuchierabu-jima Island, southern Japan

Reproductive behaviors of the largemouth triplefin Ucla xenogrammus were observed on reefs of Kuchierabu-jima Island, southern Japan. Males exclusively maintained home ranges including spawning sites on vertical walls of overhanging reefs where filamentous algae were densely distributed. Females visited a male's home range to release adhesive eggs into the dense algae. Males guarded multiple egg clutches, but rarely showed fanning behaviors or mouth cleaning to the eggs. Aquarium experiments showed that guarding males had no significant effect on egg development. Because of the favorable water exchange conditions around their spawning sites, male U. xenogrammus could avoid the energy costs for egg care.     

Reproduction of the introduced oyster Crassostrea gigas (Bivalvia: Ostreidae) cultured on rafts in Spain

The oyster Crassostrea gigas was introduced in Spain for aquaculture purposes; however, until now, it is not known whether populations are established in the wild, being necessary to define whether this species is spawning and which environmental variables trigger this process. The influence of environmental parameters on the reproduction of C. gigas was evaluated from January 2008 to October 2009 with oysters grown on a raft in the Ría de Arousa (Galicia, NW Spain). Temperature and chlorophyll a are directly correlated to sexual maturation. Oysters can mature at temperatures below 14°C. The temperature necessary for spawning differs between the sexes, requiring a temperature above 15°C for males and 18°C for females. Females had a single massive spawn between June and September, while males had partial spawning from May to December with two peaks, one in May–September and another in October–December, with the second peak more pronounced. The first spawning peak is related to high temperatures and concentrations of chlorophyll a, and the second spawning peak is mainly related to the food availability in the water. The spawning asynchrony may be impeding establishment of wild C. gigas populations in Spain.