Importance of sandy bottoms in coral reefs to the oscillation of daily rhythms in the tropical wrasse Halichoeres trimaculatus

Most wrasse species swim during the day and bury themselves in the sandy bottoms of shallow reefs at night. This study aimed to evaluate the importance of sandy bottoms to the day-active/night-inactive rhythmicity of the tropical wrasse Halichoeres trimaculatus. Actogram analysis revealed that fish were active during the photophase and inactive during the scotophase in aquariums with both sandy and bare bottoms. When fish were kept in aquariums with bare bottoms, rhythmicity was maintained under constant dark conditions (DD) but became obscured under constant light conditions (LL), suggesting that a day-active/night-inactive rhythmicity is regulated by the circadian system. Robust fluctuations in Period1 (wPer1) and Period2 (wPer2) expression were observed in the pectoral fin tissue under light–dark conditions (LD). Similar fluctuations in wPer1 expression persisted under DD. When fish were kept under LD conditions for 7 days and then DD for 20 days, the emergence of fish from the sandy bottom was delayed gradually. At the same time, the peak time of wPer1 expression under DD was retarded from 06:00 to 10:00. Although wPer2 expression was dampened under DD, it increased after exposing fish to light. These results suggest that wPer1 and wPer2 are differentially involved in the day-active/night-inactive rhythmicity, and that blocking light with a sandy bed at night and exposing fish to light during emergence in the morning play important roles in maintaining consistent activities in wrasse species.     

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.     

Relationships between four novel ceratomyxid parasites from the gall bladders of labrid fishes from Heron Island, Queensland, Australia

Ceratomyxid parasites from the gall bladder of fishes from the family Labridae were examined for their taxonomic identity and their relatedness to other species of myxozoans. This paper describes four novel species Ceratomyxa choerodonae n. sp. from Choerodon cyanodus; Ceratomyxa cheilinae n. sp. from Cheilinus chlorourus; Ceratomyxa oxycheilinae n. sp. from Oxycheilinus digramma; and Ceratomyxa thalassomae n. sp. from Thalassoma lunare. Each species is characterised morphologically and small subunit (18 S) rDNA sequences were used in molecular phylogenetic analyses. Comparison of the small subunit rDNA sequences revealed four distinct species even though morphological differences indicated the presence of only two morphologically distinctive spore types. Phylogenetic analyses revealed that the ceratomyxids from labrid fishes did not form a clade to the exclusion of all other myxosporeans and provides evidence that host relatedness is not a good character to discriminate between species within the genus Ceratomyxa.     

Courtship and spawning sounds in bird wrasse Gomphosus varius and saddle wrasse Thalassoma duperrey

Acoustic signals from the bird wrasse Gomphosus varius and saddle wrasse Thalassoma duperrey were recorded on coral reefs in Hawaii. Terminal phase males in both species emit two types of pulse trains (type I and type II). Type I pulses were produced during spawning and courtship, while type II pulses were associated only with courtship behaviours. Gomphosus varius type I pulses were of lower frequency than T. duperrey type I pulses (271 v. 840 Hz) and were of narrower band. Discriminant function analyses revealed interspecific differences between type I pulse trains and individual pulses of both types. This study is the first documentation of courtship and spawning sounds in sympatric labrids and shows divergence in acoustic signals.     

Reproductive biology of an odacine labrid, Odax pullus

The sexual ontogeny of butterfish Odax pullus was examined in the Hauraki Gulf of New Zealand through histological analysis of gonad material, size and age information and seasonal patterns of sexual maturation. The patterns of gonad development and schedules of male recruitment were established and sexual ontogeny of O. pullus was diagnosed as monandric protogyny, with all males developing from mature females after female-to-male sex reversal. All individuals underwent an immature female phase before maturing as functional females at 228·7-264·8 mm fork length (L(F) ) and at 1·1-1·5 years of age, and there was no evidence of a juvenile bisexual phase. Degenerating mature oogenic elements were found in the gonad lumen of individuals with developing spermatogenic tissue, providing histological evidence for functional protogyny. Sex change was estimated to occur at 359-379 mm L(F) and 2-3 years of age. The diagnosis of monandric protogyny for O. pullus coincided with the pattern of sexual ontogeny seen in the majority of labrids, particularly those of the same clade (tribe Hypsigenyini) and contrasted with that seen in a number of other temperate labrids. This study suggests that the protogynous mode of sexual development in O. pullus is likely to be lineage-specific, i.e. associated with the phylogeny of labrid sexual development, and is not constrained by environmental effects on the evolution of sex change in temperate regions.     

Hypometabolism in torpid goldsinny wrasse subjected to rapid reductions in seawater temperature

Goldsinny Ctenolabrus rupestris were subjected to rapid, environmentally realistic, reductions in temperature at 2° C increments from 10 to 4° C over a 3-day period in full-strength sea water. In separate experiments, oxygen uptake measurements and ultrasound recordings of heart rate and opercular motion were carried out at regular intervals over the same temperature regime. Mean oxygen uptake rates fell from 0.042 to 0.028 ml O₂ g⁻¹ h⁻¹ between 10 and 6° C respectively (Q₁₀=2.71). Between 6 and 4° C mean rates decreased from 0.028 to 0.008 ml O₂ g⁻¹ h⁻¹ (Q₁₀=542). Mean opercular motion and heart beat rates decreased from 49.5 and 60.3 beats min⁻¹ respectively at 10° C to 18.7 and 18.0 beats min⁻¹ respectively at 4° C. Most goldsinny subjected to 4° C were observed in a torpid state and would not react to external stimulation. Opercular motion was erratic at 4° C and would at times cease altogether for periods up to 1.3 min duration. Heart movement was diffcult to detect at 4° C and may also have ceased for prolonged periods. Q₁₀ values for opercular motion and heart beat rates recorded between 6 and 4° C were 6.39 and 24.52 respectively compared with values of 2.42 and 2.93 respectively recorded between 10 and 8° C. Such large depressions in metabolism appear not to have been reported previously for a marine fish species. No goldsinny mortalities were recorded at any temperature. The possibility that hypometabolic torpor is an adaptive strategy for goldsinny survival at low environmental temperatures is discussed.     

Phylogenetic systematics and biomecha cs in ecomorphology

Synopsis Research in all fields of biology increasingly uses phylogenetic systematics to interpret biological data in an evolutionary context. It is becoming widely accepted that comparative studies of the correlation of biological features, such as ecomorphological studies, must frame their analyses within the context of a phylogenetic hierarchy rather than treating each taxonomic unit as an independent replicate. Recent methods for the interpretation of ecological and functional data in the framework of a phylogeny can reveal the degree to which ecomorphological characters are correlated with one another, and are congruent with hierarchical cladistic groups. An example of the ecomorphology of labrid fishes is used here to illustrate the application of several of these methods. The structural design and mechanics of the jaws of labrids are tested for ecomorphological associations with the natural diets of these fishes. Methods for analysis of the correlated evolution of both discrete and continuous quantitative characters within a phylogeny are practiced on a single ecomorphological data set. Techniques used include character coding, character mapping, phylogenetic autocorrelation, independent contrasts, and squared change parsimony. These approaches to diverse biological data allow the study of ecomorphology to account for patterns of phylogenetic ancestry. Biomechanics or functional morphology also plays a vital role in the determination of ecomorphological relationships by clarifying the mechanisms by which morphologies can perform behaviors important to the organism's ecology. The synthesis of systematics with biomechanics is an example of interdisciplinary study in which information exchange can elucidate patterns of evolution in ecomorphology.     

Hogfish Lachnolaimus maximus (Labridae) confirmed in the south‐western Atlantic Ocean

Based on material deposited in collections, photographic records and other reports from fishermen and divers, the occurrence of the hogfish Lachnolaimus maximus (Labridae) is confirmed in the south‐western Atlantic Ocean, near the Brazilian coast as far south as southern Brazil. The recognized range of this species should therefore be extended c. 3000 km further south.     

The influence of habitat and behavioural interactions on the local distribution of the wrasse,Pseudolabrus celidotus

Synopsis The temperate wrasse, Pseudolabrus celidotus (Labridae), was studied in a shallow rocky reef habitat to asses how ecological and behavioural factors influence its within habitat patterns of distribution. Emphasis was placed on examining the mechanisms underlying size/age related changes in dispersion and habitat use. Juveniles (< 100 mm SL) were found to be aggregated whereas adults tended to be more randomly dispersed. This pattern appeared to be a product of both (a) ecological, and (b) behavioural factors. (a) Juveniles were closely associated with shelter (macro-algae) which was located in patches throughout the habitat. Their local distribution was probably not related to the distribution of their major prey items. Shelter dependence appears to decrease with growth and fish switched from feeding on micro-crustaceans present in macro-algae to those associated with bare rock — coralline turf areas. Adults foraged throughout larger home ranges, but fed preferentially in microhabitats where their prey items (e.g. bivalves) were most abundant. (b) Juveniles tended to aggregate into loose foraging schools. This tendency declined with age and was associated with a corresponding increase in the rate of aggressive interactions among individuals of a cohort. Consequently, individuals of the same size became more spaced out as they grew. Between cohort association or aggression was rare and apparently unimportant in determining local patterns of distribution. Many interspecific foraging associations and aggressive interactions were recorded. However, with the probable exception of interspecific territoriality by the blenny Forsterygion varium, these behaviours probably had only a transitory influence on the distribution of the wrasse.     

Evolutionary dynamics of complex biomechanical systems: an example using the four-bar mechanism

Like many phenotypic traits, biomechanical systems are defined by both an underlying morphology and an emergent functional property. The relationship between these levels may have a profound impact on how selection for functional performance is translated into morphological evolution. In particular, complex mechanical systems are likely to be highly redundant, because many alternative morphologies yield equivalent functions. We suggest that this redundancy weakens the relationship between morphological and functional diversity, and we illustrate this effect using an evolutionary model of the four-bar lever system of labrid fishes. Our results demonstrate that, when traits are complex, the morphological diversity of a clade may only weakly predict its mechanical diversity. Furthermore, parallel or convergent selection on function does not necessarily produce convergence in morphology. Empirical observations suggest that this weak form-function relationship has contributed to the morphological diversity of labrid fishes, as functionally equivalent species may nevertheless possess morphologically distinct jaws. We suggest that partial decoupling of morphology and mechanics due to redundancy is a major factor in morphological diversification.