Gonadal development and an indication of functional protogyny in the Indian damselfish (Dascyllus carneus)

The objective of this study was to determine the sexual pattern of the Indian dascyllus Dascyllus carneus . After an initially undifferentiated state, gonads of D. carneus developed an ovarian lumen and primary growth stage oocytes, and subsequently cortical-alveolus stage oocytes. From ovaries with cortical-alveolus stage oocytes and from more developed ovaries, some gonads redifferentiated into testes. From a sample of 163 individuals, two had a gonad containing degenerating vitellogenic oocytes and proliferating spermatogenic tissue, nine had a gonad containing degenerating cortical-alveolus stage oocytes and spermatogenic tissue, and five had a gonad with degenerating primary growth stage oocytes and spermatogenic tissue. The size of these individuals overlapped greatly with the size range of mature females, suggesting that at least in some individuals, redifferentiation toward a testis occurred after spawning as females. This indicates that D. carneus is a functional, diandric protogynous hermaphrodite. Removal of a dominant male(s) did not induce a sex change in any of the ranking females in the laboratory and field groups. There was no difference in the number of chases and signal jumps performed by the ranking female between control and experimental field groups, or before and after removal of the male. However, the sizes of the ranking females were at or beyond the size range of individuals with a mixed-stage gonad, suggesting that the developmental window for female-to-male sex change may not be open ended. In 41 of 43 field groups, in which sex of fish was determined histologically or by the shape of the urogenital papilla, one to several highest size ranks were occupied by males, followed by one to several females. Mature males, however, were not limited to the highest ranks and occurred at various lower size ranks within groups. Individuals with a mixed-stage gonad also occupied various size ranks within groups.     

Genetic relatedness in groups of the humbug damselfish Dascyllus aruanus: small, similar-sized individuals may be close kin

Kin selection plays an important role in the evolution of social behaviour in terrestrial systems. The extent to which kin selection influences the evolution of social behaviour in marine systems is largely unexplored. Generally, it is considered that kin selection is irrelevant in marine systems, because it is assumed that the dispersing larval phase of marine organisms will break up kin associations. Here, we challenge this assumption and investigate the opportunity for kin selection in a coral reef fish: the humbug damselfish Dascyllus aruanus . This fish lives in groups composed of a large male and a number of smaller females and nonbreeders. We use 10 polymorphic microsatellite loci to assess the relatedness of 265 individuals from 35 groups. The mean coefficient of relatedness among group members is 0.01 ± 0.04, suggesting that individuals are not associated with close relatives. However, the distribution of pairwise relatedness of individuals within groups has an overabundance of positive values, and indicates that there might be 35 pairs of close relatives within groups. Further analyses reveal that close relatives likely are similar in size and small in size, suggesting that they might have recruited together. We conclude that it is possible for kin selection to operate in D. aruanus , but kin recognition will be a prerequisite for such selection. This study reveals that individuals can be associated with close relatives, and there is a hidden potential for kin selection, during certain parts of the life cycle of coral reef fishes.     

Isolation and characterization of 13 polymorphic nuclear microsatellite primers for the widespread Indo-Pacific three-spot damselfish, Dascyllus trimaculatus, and closely related D. auripinnis

A set of 13 simple sequence repeat markers was developed from D. trimaculatus genomic DNA, tested for D. auripinnis and characterized using 40 individuals per species. All the loci were polymorphic with a number of alleles ranging from three to 30. Observed heterozygosities varied from 0.23 to 0.89 for D. trimaculatus and from 0.11 to 0.85 for D. auripinnis. Early results show that these will be powerful markers for the study of ecological and evolutionary mechanism in this coral reef fish species complex.     

Selective mortality of a coral reef damselfish: role of predator–competitor synergisms

Phenotypic variability within cohorts of juvenile organisms can serve as the basis for selective mortality. Previous studies have demonstrated the important role that predators play in this process but not the impact of competitors on selective predation. We use a combination of lab and field studies to evaluate the effect of the presence of adult competitor damselfish (Dascyllus aruanus and Pomacentrus moluccensis; family Pomacentridae) on the selective mortality of newly-arrived (settled) lemon damselfish (P. moluccensis) by resident predator fishes (Pseudochromis fuscus Pseudochromidae and Cheilodipterus quinquelineatus Apogonidae). Lab trials consisted of mesocosm experiments in which the behaviour, mortality, and physiological condition (measured as lipid content) of surviving P. moluccensis settlers from each of three treatments: (1) predators absent, (2) predators present, and (3) predators and competitors present, were compared. The field study involved stocking newly settled P. moluccensis on natural bommies (patch reefs) which had either been subject to a partial removal of resident fish (predators and competitors) or left alone. Results indicated there was very strong condition-based selective mortality in both the lab and field trials. In both cases there was a strong positive relationship between mortality and the lipid content of surviving fish; implying low-condition fish were selectively removed. The mesocosm trials indicated that the strength of mortality as well as condition selectivity was higher when competitors were present than when they were absent. Behavioural observations in the mesocosm study suggest that attention by juvenile P. moluccensis to the movements and occasional chases of the competitors (especially D. aruanus) reduced their vigilance to the predators. These results suggest the important and interactive roles which condition of newly settled reef fish and interspecific competition can play in the outcomes of post-settlement predation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Molecular phylogeny of the humbug damselfishes inferred from mtDNA sequences

The damselfish genus Dascyllus comprises nine species of both large- and small-bodied fishes distributed over the entire Indo-West Pacific. Most members of the genus have polygynous mating systems with protogynous sex change, while others are promiscuous with no sex change. Hypotheses linking presumed phylogenetic relationships with body size, sex change and mating structure have been proposed previously. However, lack of a strong phylogenetic hypothesis has prevented the careful testing of such hypotheses. In this study, the phylogenetic relationships between Dascyllus species based on mitochondrial DNA sequences (cytochrome b and 16SrRNA) have been established. The data also shed light on the relationship between mating structure and body size, as well as on the complex biogeographical patterns of the genus.     

A NEW SOUND TRAP,AND OBSERVATIONS ON THE MIGRATORY AND ACOUSTIC BEHAVIOUR OF THE FIELD CRICKET TELEOGRYLLUS COMMODUS (WALKER)

ABSTRACT

A new sound trap for capturing male and female crickets attracted to the calling song of the male is described. Major advantages of the trap are its portability and effectiveness. It was designed to operate in conjunction with a previously described cricket-song generator. The trap is compared with other designs and the acoustic and migratory behaviour of crickets revealed by sound trapping are discussed.     

Ultraviolet Radiation Absorbance by Coral Reef Fish Mucus: photo-protection and Visual Communication

Tropical reef fishes are exposed to high levels of damaging ultraviolet radiation. Here we report the widespread distribution of both UVA- and UVB-absorbing compounds in the epithelial mucus of these fishes. Mucus from 137 reef fish species was examined by spectrophotometry and 90% were found to have strong absorbance peaks between 290 and 400nm. Most fish species (78%) had more than one peak, that suggests a broad-band ultraviolet screening function for their mucus. Thalassoma duperrey, a tropical wrasse, was able to alter the absorbance of its epithelial mucus in response to both naturally and experimentally manipulated UV regimes. Visual modeling suggests that a fish with UV vision, such as Dascyllus albisella, could detect the changes in mucus spectra of T. duperrey that occurred in these experiments.     

ON THE EXTRACTION OF SOME TIME DEPENDENT PARAMETERS OF AN ACOUSTIC SIGNAL BY MEANS OF THE ANALYTIC SIGNAL CONCEPT. ITS APPLICATION TO ANIMAL SOUND STUDY

ABSTRACT

When studying the acoustic signals of animals, it is often necessary to obtain the precise time structure of the frequency. It is also useful to extract the envelope of a signal or to modify a signal to obtain its frequency modulated part. This can be achieved digitally using the analytic signal concept.

We deal here with the method. Definition and computation are described, its application is discussed and the performances are compared to those of sonagraph and zero- crossing methods. This paper presents a method enabling precise AM and FM analysis of different animal vocalisations. The method has also been used for the purpose of synthesis by extracting the frequency modulated part of a signal. It is found to be a powerful means of modifying some parameters of a natural signal without altering other features.     

Distinct patterns of hybridization across a suture zone in a coral reef fish (Dascyllus trimaculatus)

Hybrid zones are natural laboratories for investigating the dynamics of gene flow, reproductive isolation, and speciation. A predominant marine hybrid (or suture) zone encompasses Christmas Island (CHR) and Cocos (Keeling) Islands (CKE), where 15 different instances of interbreeding between closely related species from Indian and Pacific Oceans have been documented. Here, we report a case of hybridization between genetically differentiated Pacific and Indian Ocean lineages of the three‐spot dascyllus, Dascyllus trimaculatus (Rüppell, 1829). Field observations indicate there are subtle color differences between Pacific and Indian Ocean lineages. Most importantly, population densities of color morphs and genetic analyses (mitochondrial DNA and SNPs obtained via RADSeq) suggest that the pattern of hybridization within the suture zone is not homogeneous. At CHR, both color morphs were present, mitochondrial haplotypes of both lineages were observed, and SNP analyses revealed both pure and hybrid genotypes. Meanwhile, in CKE, the Indian Ocean color morphs were prevalent, only Indian Ocean mitochondrial haplotypes were observed, and SNP analysis showed hybrid individuals with a large proportion (~80%) of their genotypes assigning to the Indian Ocean lineage. We conclude that CHR populations are currently receiving an influx of individuals from both ocean basins, with a greater influence from the Pacific Ocean. In contrast, geographically isolated CKE populations appear to be self‐recruiting and with more influx of individuals from the Indian Ocean. Our research highlights how patterns of hybridization can be different at scales of hundreds of kilometers, due to geographic isolation and the history of interbreeding between lineages.