Thalassoma Bifasciatum Research Articles

The polychaete Cirriformia punctata is chemically defended against generalist coral reef predators

The Caribbean cirratulid polychaete, Cirriformia punctata (Grube, 1856), is bright orange and burrows just below the surface of fine carbonate sand with only its filamentous tentacles and gills exposed to potential predators. In addition to its conspicuous coloration, C. punctata lacks obvious structural and morphological defenses. We hypothesized that C. punctata protects itself from predation using secondary metabolites as a chemical defense. Feeding bioassays were performed using whole worms to determine palatability against two generalist coral reef predators: the bluehead wrasse, Thalassoma bifasciatum, and the brown anemone, Aiptasia sp. Additionally, assays were conducted with hermit crabs of the genus Paguristes, but with limited success. In all assays, C. punctata was unpalatable to consumers. The tentacles and body of the worm were separately assayed using T. bifasciatum to determine whether the defensive mechanism was differentially allocated to body regions that are differently exposed to potential predators. Both the tentacles and body of C. punctata were unpalatable to T. bifasciatum, indicating no specific allocation of defenses. Crude organic extracts of whole C. punctata were unpalatable to T. bifasciatum, confirming that the worm defense is chemical rather than morphological. Chemical defenses of Cirriformia spp. appear to be generally effective against taxonomically diverse potential consumers.

Behavioral and energetic costs of group membership in a coral reef fish

Animals in social aggregations often spend more time foraging than solitary conspecifics. This may be a product of the relative safety afforded by aggregations: group members can devote more time to foraging and less time to antipredator behaviors than solitary animals (the "risk reduction" effect). All else being equal, risk reduction should result in higher food intake for grouped animals. However, intragroup competition may force group members to spend more time foraging in order to obtain the same food ration as solitary individuals (the "resource competition" effect). We compared these opposing explanations of foraging time allocation in a coral reef fish, bluehead wrasse (Thalassoma bifasciatum). Aggregations of juvenile bluehead wrasse experience safety-in-numbers, and preliminary observations suggested that juveniles in aggregations spent more time foraging for copepods in the water column than solitary juveniles. However, the risk reduction and resource competition hypotheses are indistinguishable on the basis of behavioral observations alone. Therefore, we collected behavioral, dietary, and growth data (using otolith growth rings) for bluehead wrasse at multiple reefs around a Caribbean island. Despite spending more time foraging in the water column, grouped fish did not capture more prey items and had slower growth rates than solitary fish. Thus, the increased foraging time of grouped fish appears to reflect resource competition, not risk reduction. This competition may limit the size and frequency of aggregations among juvenile bluehead wrasse, which have been shown to experience reduced mortality rates in larger groups. Bluehead wrasse recruits also spent less time foraging but grew faster at sites where planktonic copepod prey were more abundant. This suggests the possibility that large-scale spatiotemporal variability in the abundance of planktonic copepods over coral reefs may produce corresponding variability in the dynamics of reef fish populations.

A multi-locus assessment of connectivity and historical demography in the bluehead wrasse (Thalassoma bifasciatum)

The pelagic larval stage of most coral reef fishes might allow extensive dispersal or, alternatively, some level of local recruitment might be important. Molecular markers can be used to obtain indirect estimates of dispersal to evaluate these alternatives, yet the extent of gene flow among populations is known for only a small number of species. The use of such markers must take into account the properties of the markers and the demographic history of the population when making inferences about current gene flow. In the Caribbean bluehead wrasse, Thalassoma bifasciatum, previous studies have found both substantial levels of local recruitment, in studies interpreting otolith microchemistry and, conversely, a lack of genetic differentiation inferred from mitochondrial DNA (mtDNA) restriction-fragment length polymorphism (RFLP) data and allozymes. However, if subtle differentiation exists, larger sample sizes and highly variable markers may be required to discern it. Here we present results from mitochondrial control region sequence and microsatellite data that indicate a lack of genetic differentiation at both small and large spatial scales. However, historical processes, such as changes in population size, may have affected the current distribution of genetic variation.

The Role of Vanadium in the Chemical Defense of the Solitary Tunicate, Phallusia nigra

Ascidians (sea squirts) may defend themselves from predators, biofouling competitors, and bacterial infection by producing secondary metabolites or sequestering acid, but many species also accumulate heavy metals, most notably vanadium. The defensive functions of heavy metals in ascidians remain unclear, and to this end, the solitary Caribbean tunicate, Phallusia nigra, was studied to localize vanadium in its tissues and to assess the defensive properties of vanadium-containing compounds. As determined by flame atomic absorption spectroscopy, the internal tissues and blood contained the highest vanadium concentrations (mean values of 2280 and 1886 ppm dry mass, respectively), followed by the tunic surface (871 ppm dry mass). Results of laboratory feeding assays with the bluehead wrasse, Thalassoma bifasciatum, confirmed outcomes of past studies that demonstrated that vanadyl sulfate (VOSO4.6H20) and sodium vanadate (Na3VO4) were unpalatable to fish, although these salts do not accurately reflect the chelation environment or oxidation state of vanadium in living tunicates. Fresh preparations of whole tunic, internal tissues, and blood were unpalatable to fish, but freezing and thawing of internal tissues and blood rendered them palatable. Crude organic extracts of whole tunic and internal tissues contained vanadium metabolites (225 and 750 ppm dry mass, respectively) and were palatable to T. bifasciatum; crude extracts also exhibited no antimicrobial effects against a panel of four marine bacteria known to be pathogens of marine invertebrates (Vibrio parahaemolyticus, Vibrio harveyi, Leucothrix mucor, and Deleya marina). Nonacidic vanadium (+3) complexes neither deterred predation nor inhibited microbial growth, whereas acidic aqua vanadium (+3 and +4) complexes were unpalatable to 7 bifasciatum and exhibited antimicrobial activity. Difficulties in decoupling low pH from oxidation state and chelation environment of vanadium prevent definitive conclusions about the importance of some vanadium metabolites, but low pH appears to be the principal agent of chemical defense for P. nigra.

A Comparison of Fish Assemblages Among Five Habitat Types Within a Caribbean Lagoonal System

Fish assemblages associated with patch reefs, rubble, seagrass, algal plain, and sandy habitats types were studied at St. Croix's Southeastern barrier reef lagoon using underwater visual census techniques. Higher species richness and fish density were observed over patch reefs/rubble habitat followed by seagrass, algal plain, and unvegetated sandy habitat types. Thalassoma bifasciatum, Haemulon flavolineatum, and Acanthuras chirurgus were the most common fishes in highly structured habitat types (patch reef, rubble). Halichoeres bivittatus, Sparisoma radians, newly settled grunts (l.e., Haemulon spp.), and juveniles of Ocyurus chrysurus were mainly associated with vegetated habitat types (seagrass, algal beds), while Xyrichtys martinicensis and Coryphopterus glaucofraenum were common over unvegetated sandy habitat types. Cluster analysis among backreef lagoon habitat types based on the entire fish density data showed distinct associations of fish assemblages by habitat type, regardless of season. Fish assemblages in the more structured habitat types were similar to each other but different from unstructured vegetated, and unvegetated habitat types. These results suggest that differences in fish species richness and density in the backreef lagoon are related to habitat type. The ecological importance and need for protection of backreef lagoon habitat types are discussed in relation to their potential role as nurseries for many fish species.

Influence of condition on behavior and survival potential of a newly settled coral reef fish, the bluehead wrasse Thalassoma bifasciatum

For newly settled coral reef fishes, survival advantages may be associated with specific early life history traits or condition levels that lead to differences in behavior. To identify physiologi- cal and behavioral characteristics associated with different condition levels, bluehead wrasse Thalas- soma bifasciatum recruits were collected immediately after settlement from reefs in the upper Florida Keys, USA, and transported to the laboratory for experimental analysis. Quantification of swimming capabilities was coupled with otolith analysis to identify early life history traits associated with swim- ming performance. Fish with the highest critical swimming speeds were those that grew faster as lar- vae, had shorter pelagic larval durations, and were smaller at settlement, although these individuals represented only 10% of the total sample. To further investigate condition-associated behaviors, a feeding treatment established fish of 2 different condition levels for comparison. Recruits fed for 1 wk at higher levels grew faster, had greater standardized weight (Fulton's condition factor), and swam faster than food-deprived recruits. In additional behavioral trials, high condition recruits evaded a simulated predator threat at faster speeds than the low condition recruits. High condition fish also exhibited less risk-taking behavior by sheltering more in the presence of a predator threat and con- suming less food. For both high and low condition recruits, the number that sought shelter increased and food consumption rates decreased in the presence of a predator threat. These results link early life history traits and physiology with associated condition-based differences in behavior, likely underlying the observation that mortality in T. bifasciatum is frequently selective for condition.

Aromatase immunoreactivity in the bluehead wrasse brain, Thalassoma bifasciatum: Immunolocalization and co-regionalization with arginine vasotocin and tyrosine hydroxylase

Sex steroid hormones regulate various neural functions that control vertebrate sociosexual behavior. A number of sex steroids can be synthesized de novo in the brain, including estrogens by the enzyme aromatase. Aromatase, the neuropeptides arginine vasotocin/vasopressin, and the monoamine neurotransmitter dopamine have all been implicated in the control of male sexual and aggressive behavior in a variety of vertebrates. This study examined the expression of brain aromatase in the bluehead wrasse (Thalassoma bifasciatum), a teleost fish that exhibits socially controlled behavioral and gonadal sex change. We used immunocytochemistry (ICC) to characterize distributions of aromatase-immunoreactive (ir) cells, and to examine their relationship with AVT-ir neurons and tyrosine hydroxylase-ir (TH-ir) neurons in key sensory and integrative areas of the brain of this species. Aromatase-ir appeared to be in glial cell populations, and was found in the dorsal and ventral telencephalon, the preoptic area of the hypothalamus, and the lateral recess of the third ventricle, among other brain areas. Aromatase-ir fibers are closely associated with AVT-ir neurons throughout the preoptic area, indicating the potential for functional interactions. Aromatase-ir cell bodies and fibers were also co-regionalized with TH-ir neurons, suggesting possible interaction between the dopaminergic system and neural estrogen production. The presence of aromatase in brain regions important in the regulation of sexual and aggressive behavior suggests that local estrogen synthesis could regulate sex change through effects on signaling systems that subserve reproductive behavior and function.

A social basis for the development of primary males in a sex-changing fish

An example of alternative male strategies is seen in diandric protogynous (female first) hermaphrodites, where individuals either mature directly as male (primary males) or first reproduce as female and then change sex to male (secondary males). In some sex-changing fishes, the testes of primary males appear anatomically similar to those of non-sex-changing species, whereas the testes of secondary males have anatomical evidence of their former ovarian function. Here, we provide evidence that in the bluehead wrasse, Thalassoma bifasciatum, these strikingly different male phenotypes arise from differences in the ontogenetic timing of environmental sex determination, timing that can be experimentally altered through changes in the social circumstances. Juveniles differentiated almost exclusively as females when reared in isolation, regardless of whether they were collected from a reef with a high proportion of primary males or from a reef with a low proportion of primary males. In contrast, one individual usually differentiated as a primary male when reared in groups of three. Our results indicate that primary males of the bluehead wrasse are an environmentally sensitive developmental strategy that has probably evolved in response to variation in the reproductive success of primary males in populations of different sizes.

Distribution of behaviours and species interactions within home range contours in five Caribbean reef fish species (Family Labridae)

This study investigated the distribution of behaviours and species interactions within home range contours in five Caribbean labrid species: Halichoeres bivittatus, H. garnoti, H. maculipinna, H. poeyi, and Thalassoma bifasciatum. For this study, contours were defined as: (a) 30%—the core use area, (b) 30–75%—the intermediate activity area, and (c) 75–95%—the peripheral activity area. Behaviours analyzed for this study included: (i) feeding (=biting the substrate or chewing), (ii) chased by pomacentrids, (iii) swimming alone, (iv) swimming with other fishes, and (v) all activities with other fishes. Fifty-nine percent of Halichoeres bivittatus observed showed a higher frequency than expected being chased by pomacentrids in the peripheral region of their home ranges. Halichoeres garnoti showed a lower frequency than expected swimming with other individuals in their core use area, and 64% of the individuals observed showed a higher frequency than expected being chased by pomacentrids in the peripheral region. In general, H. maculipinna exhibited a random distribution of behaviours throughout their home range areas, with a non-significant trend for more agonistic interactions with pomacentrids in peripheral regions. Halichoeres poeyi and T. bifasciatum showed higher frequencies than expected being chased by pomacentrids in the peripheral regions. Overall, the non-random distribution of agonistic interactions with pomacentrids throughout home range areas suggests that the presence or prior residence of territorial pomacentrids on coral reefs may modify the post-settlement selection of home range areas by these labrid species.

Environmental variability, early life-history traits, and survival of new coral reef fish recruits

For benthic marine organisms with complex life cycles, conditions experienced by pelagic larvae can influence juvenile survival. Trait-specific selective mortality has been documented in the laboratory and field, yet our knowledge of the factors contributing to the existence, strength, and consistency of natural selective mortality is limited. We compiled previously published and unpublished data on the common Caribbean coral reef fish, Thalassoma bifasciatum, recruiting to Barbados, West Indies, and the upper Florida Keys to examine how environmental variability during pelagic larval life influences the distribution of early life-history traits exhibited by new recruits. We explored how the scope of variability in otolith-derived traits such as larval growth, pelagic larval duration (PLD), size and condition at settlement, and early juvenile growth influences the degree to which mortality of juveniles is selective. At both locations, contrasting oceanographic conditions (periodic passage of large low-salinity North Brazil Current [NBC] rings near Barbados and seasonal variation in water temperature at Florida) led to significant differences in the early life-history traits of recruits. Mortality was most frequently selective for the two most variable traits, condition at settlement and early juvenile growth. Environmental variability (including variation in predation pressure and stress-inducing conditions) also likely influences juvenile mortality and consequently the degree to which selective loss of particular traits occurs. As we begin to better understand the spatial, temporal, and species-specific circumstances in which events occurring during larval life influence juvenile performance, studies must also be extended to examine how these processes are translated into adult fitness.

Weak genetic structure indicates strong dispersal limits: a tale of two coral reef fish

The extent of dispersal by pelagic larvae in marine environments, including coral reefs, is central for understanding local population dynamics and designing sustainable marine reserves. We present here the first example of a clear stepping-stone genetic structure throughout the Caribbean basin for a common coral reef species, the French grunt (Haemulon flavolineatum). Analysis of microsatellite DNA markers indicated that French grunt population structure may be characterized by overlapping populations throughout the Caribbean, influenced by independent population dynamics but with no fixed geographical boundaries. In addition, different spatial genetic patterns were found in different oceanographic regions. A second species, the bluehead wrasse (Thalassoma bifasciatum), has a much longer pelagic larval duration than French grunts and showed no explicit spatial pattern of genetic variation. This finding is concordant with the hypothesis of a positive relationship between larval dispersal and duration in the plankton. While the magnitude of the genetic signal of population structure in French grunts was very low (F(ST) approximately 0.003), the pattern of isolation-by-distance throughout the Caribbean indicated considerable population structure with important ecological and conservation significance.

Temperature-mediated variation in early life history traits and recruitment success of the coral reef fish Thalassoma bifasciatum in the Florida Keys

Thirteen cohorts of the Caribbean reef fish Thalassoma bifasciatum were collected over 4 yr (2000 to 2003) in the upper Florida Keys, USA. Juvenile fish were censused and collected from replicate reefs shortly after settlement. The otoliths were examined to obtain early life history information such as timing of spawning, larval growth, pelagic larval duration, size-at-age, timing of set- tlement, and juvenile age and growth. Mean water tem- perature over the reef during the larval period explained 78% of the variation in larval growth among cohorts. Faster-growing warm-water fish had shorter pelagic lar- val durations (PLD), and larval growth explained 85% of the variation in PLD. Relative (otolith) size-at-settlement was a function of larval growth as well as PLD: settling larvae were largest at intermediate water temperatures. Early juvenile growth was also directly related to water temperature, which enabled smaller warm-water settlers to grow rapidly and eventually exceed juvenile size-at- age of the cooler-water cohorts. Cohorts encountering intermediate water temperatures remained the largest throughout early juvenile life on the reef. The relative size of recruitment events could not be explained by any larval or juvenile trait, nor by water temperature. Recruitment was generally low for cool-water cohorts but quite vari- able among warm-water cohorts. This may be due to in- creased difficulty in sustaining high growth rates in warm water (i.e. beyond a threshold temperature of 28.5°C) or the interference of mesoscale advection processes. When 4 cohorts that settled during the passage of mesoscale eddies were omitted from the analysis, 61% of the varia- tion in recruitment magnitude could be explained by water temperature alone. The dynamic oceanographic setting of the Florida Keys may obscure the relationship between seasonal water temperature, early life history traits, and magnitude of recruitment events.

Consistent long-term spatial gradients in replenishment for an island population of a coral reef fish

The population replenishment of marine organisms is routinely characterized as highly variable and unpredictable in space and time. Using island-wide recruitment surveys of a common coral reef fish, the bluehead wrasse Thalassoma bifasciatum, in 6 summers spanning a 12 yr period (1991 to 2003), we examined whether spatial patterns of recruitment are consistent or variable through time on St. Croix, US Virgin Islands. Despite annual fluctuations in the magnitude of replen- ishment, recruitment intensity follows a distinct and consistent spatial gradient that differs in direc- tion between the north (leeward) and south (windward) shores; recruitment declines from west to east on the north shore and east to west on the south shore. The rank ordering of sites on each shore was concordant when recruitment was either pooled across years (monthly variation) or pooled across months (annual variation). When the 2 highest recruitment sites on each shore were consid- ered alone, consistent seasonal effects were also apparent, with higher recruitment from June through August on the north shore, and higher recruitment in September on the south shore. Thus, while the magnitude of recruitment is indeed variable in space and time, its qualitative pattern is pre- dictable in this area. Results of prior investigations of larval dispersal and coastal oceanography around St. Croix shed light on the origin of the consistent recruitment patterns documented in this study. The potential for consistent spatial and temporal patterns in recruitment is an important con- sideration in the spatial management of marine resources.

The importance of the marine ornamental reef fish trade in the wider Caribbean.

The marine ornamental fish trade began in the 1930s in Sri Lanka, spread to Hawaii and the Philippines in the 1950s, and expanded to a multi-million dollar industry in the 1970s with fisheries established throughout the tropical Pacific, Indian and Atlantic Oceans. Currently, 45 countries supply global markets an estimated 14-30 million fish annually, with an import value of US$28-44 million. The largest suppliers are Indonesia and the Philippines, followed by Brazil, Maldives, Vietnam, Sri Lanka and Hawaii. In the tropical Western Atlantic, 16 countries have export fisheries, including the U.S. (Florida and Puerto Rico). The U.S. is the world's largest buyer, followed by the European Union and Japan. The global trade consists of over 1400 species of reef fishes, of which only about 25 are captive bred on a commercial scale. Damselfish, anemonefish, and angelfish constitute over 50% of the global volume; butterflyfish, wrasses, blennies, gobies, triggerfish, filcfish, hawkfishes, groupers and basselets account for 31% of the trade, and the remaining 16% is represented by 33 families. The most important fishes from the Caribbean are angelfish (six species), seahorses (two species), royal gramma, jawfish, queen triggerfish, redlip blenny, puddingwife, bluehead wrasse, and blue chromis. The Caribbean currently supplies a small percentage of the global trade in marine ornamental species, but ornamental fisheries in this region represent important emerging industries. It is critical that effective ornamental fishery management plans and regulations are developed and enforced, and fishery-dependent and fishery-independent data are collected and utilized in decision making processes to ensure sustainable ornamental fisheries throughout the region.

Testing for defensive synergy in Caribbean sponges: Bad taste or glass spicules?

Chemical and physical defenses of sessile organisms against consumers are well described for both terrestrial and marine systems. However, previous studies have focused on chemical or physical defenses in isolation, and have not considered their interaction. Marine sponges provide a model system for testing this interaction. Some sponge species produce secondary metabolites that deter predation; they may also contain siliceous spicules, but previous studies have provided little evidence that spicules in isolation offer any defense against generalist fish predators. To determine whether the two components have an additive, antagonistic, or synergistic interaction, crude organic extracts and spicules from individuals of 8 Caribbean sponge species were isolated and tested in laboratory feeding assays. These included one chemically defended reef sponge ( Agelas clathrodes) and seven known to be intermediately deterrent: six from reef habitats ( Cinachyrella alloclada, Clathria virgultosa, Cribrochalina infundibulum, Niphates digitalis, Svenzea zeai, and Xestospongia muta) and one from mangrove habitats ( Tedania ignis). Extracts and spicules were assayed at various concentrations, both individually and in combination, in laboratory feeding assays with the bluehead wrasse, Thalassoma bifasciatum. A SAS based GENMOD procedure based on an isobolographic analysis model was used for statistical comparisons. Four sponges ( A. clathrodes, C. alloclada, C. virgultosa, and one of three individuals of X. muta) showed evidence of synergisms. Of these, synergy in C. alloclada, C. virgultosa, and X. muta was caused by approximately natural concentrations of extracts and spicules. The extract of A. clathrodes was deterrent, but combination assays required nearly a 3-fold reduction in extract concentration and an 8-fold increase in spicule concentration to show the synergistic effect. Contrary to previous findings, spicules from C. infundibulum and two of three individuals of X. muta were deterrent at natural concentrations. Sponge spicules may be defensive in isolation, or may enhance chemical defenses against consumers, but the lack of synergisms for individuals in 4 of 7 species with intermediate levels of chemical defense suggests that defensive synergy is not the general rule and, when present, may be an example of an exaptation.

Post-settlement emigration affects mortality estimates for two Bahamian wrasses

Understanding the dynamics of open marine populations is inherently complex, and this complexity has led to decades of debate regarding the relative importance of pre- versus post-settlement processes in structuring these populations. Movement between patches may be an important modifier of patterns established at settlement, yet local immigration and emigration have received less attention than other demographic rates. I examined loss rates from tagged populations of juvenile wrasses (yellowhead wrasse Halichoeres garnoti and bluehead wrasse Thalassoma bifasciatum) at two sites in the Bahamas. Assuming that all losses were due solely to mortality would have significantly underestimated survivorship of yellowhead wrasse by 29% and bluehead wrasse by 14%. On average, per capita mortality and emigration rates were higher for yellowhead than bluehead wrasse, but neither demographic rate differed between sites for either species. With respect to within-species density, bluehead wrasse mortality was density-dependent at the patch reef site, but mortality rates of yellowhead wrasse were consistently density-independent. Evaluating the effects of between-species density, yellowhead wrasse mortality increased with a decrease in bluehead wrasse density, but this effect was limited to the patch reef site. Emigration rates were not a function of either within-species or between-species density, but instead varied inversely with isolation distance. Numerous previous studies of coral-reef fish, conducted on patch reefs separated by only a few meters of sand and often using untagged fish, may have confounded losses due to emigration with those due to mortality. A better understanding of the factors affecting emigration in marine fishes is important to their effective management using spatial tools such as marine protected areas.

Home range areas and activity centres in six species of Caribbean wrasses (Labridae)

In six Caribbean wrasse (Labridae) species:Halichoeres bivittatus,Halichoeres garnoti,Halichoeres maculipinna,Halichoeres poeyi,Halichoeres radiatusandThalassoma bifasciatum, home range area (AHR) was positively correlated with fish total length (LT) and this relationship was not significantly different amongH. bivittatus,H. garnoti,H. radiatusandT. bifasciatum. The data for three of these species (H. radiatuswas excluded because only juveniles were investigated) were pooled and the relationship betweenLTandAHRwas analysed for juveniles and initial phase (IP) adults separately. This analysis found that once individuals of these two species become IP adults, theAHRreached a plateau, despite continued fish growth. In a separate analysis including all six wrasse species, after accounting for differences inLTusing ANOVA, it was found that IP adults required larger areas than juveniles, and terminal phase (TP) adults required largerAHRthan IP adults. Upon analysis of the distribution of activity throughoutAHRfor all species studied, it was found that 50% of the observation points (defined as the activity centre) were found in 13 to 24% of theAHR.

Fluoxetine-treated male wrasses exhibit low AVT expression

In many species, increasing serotonergic activity can reduce aggression and reverse dominance relationships. These effects may in part be mediated through interactions with the arginine vasotocin/vasopressin (AVT/AVP) system. We tested this hypothesis in a territorial coral reef fish, the bluehead wrasse ( Thalassoma bifasciatum), by experimentally enhancing serotonergic neurotransmission, using the selective serotonin re-uptake inhibitor (SSRI) fluoxetine. Terminal phase (TP) males received 2 weeks of nightly intraperitoneal fluoxetine injections (6 μg/g body weight) and were then tested for their aggressive response to an intruder and killed to examine AVT phenotype in the preoptic area of the hypothalamus (POA), an area important to social behavior in fishes. Our previously published study demonstrated that fluoxetine-treated males are less aggressive [H.A.N. Perreault, K. Semsar, J. Godwin, Fluoxetine treatment decreases territorial aggression in a coral reef fish, Physiol. and Behav. 79 (2003) 719–724.]. Here, further study of these same fluoxetine-treated males shows approximately twofold lower AVT mRNA expression relative to saline-treated controls in all regions of the POA (all p≤0.05) without any changes in AVT- ir soma size (all p>0.4). This study experimentally supports the hypothesis that behavioral effects of SSRIs may be mediated in part through interactions with the AVT/AVP system. These results parallel findings from rodents and humans and are consistent with an indirect neurosteroidogenic rather than a solely direct serotonergic mechanism for SSRI effects on the AVT/AVP system. Furthermore, they suggest that SSRI effects on neuroendocrine function may be best modeled in animals with sensitive stress responses such as those found in nondomesticated animals.

Characterization of microsatellite multiplexes for population genetic studies of bluehead wrasse (Thalassoma bifasciatum, Pisces: Labridae)

AbstractBluehead wrasse (Thalassoma bifasciatum) are common coral reef fish found throughout the Caribbean. Larval duration in the plankton is relatively long for this species, which raises the possibility of long‐distance transport by ocean currents. Several nongenetic studies suggest, however, that most recruits were spawned locally. Determination of the relative importance of local recruitment vs. immigration for recruitment is needed for the effective management of populations and establishment of marine reserves. We characterized seven new polymorphic microsatellite loci for bluehead wrasse and optimized them into PCR multiplexes with three previously published loci to determine the level of dispersal between populations.

Multiple mechanisms of phenotype development in the bluehead wrasse

Despite having detailed information on mechanisms mediating sex-typical behavior in many species, we have little understanding of whether the same mechanisms regulate these behaviors when they are performed in the same species under different social contexts. In the five field experiments of this study of bluehead wrasses ( Thalassoma bifasciatum), a sex-changing fish, we examined the roles of arginine vasotocin (AVT) and the potent teleost androgen 11-ketotestosterone (11KT) in mediating sexual and aggressive behaviors typical of dominant males. We demonstrated that AVT appears necessary for the assumption of dominant territorial status in males and females, but is sufficient only in the socially dominant terminal phase (TP) male phenotype. Specifically, an AVP V 1 receptor antagonist prevented both TP males and females from gaining dominance over recently vacated territories. However, unlike TP males in a previous study, neither females nor initial phase males responded to AVT treatment with increases in display of TP male typical behaviors when under social conditions that inhibit sex change. Treating females with 11KT did not alter responsiveness to AVT, but did induce male coloration and courtship behavior that was not observed in oil-treated females. Combined with the results of a previous study, these results indicate that the ability of AVT to induce male-typical behavior differs among sexual phenotypes and that this differential responsiveness appears to be dependent on social context and not directly on exposure to 11KT. Furthermore, since 11KT can induce courtship behavior in females that is not affected by AVT, there may be different hormonal mechanisms mediating courtship behavior under different social contexts.