Cécile Fauvelot

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.

Distribution of Noah’s giant clam, Tridacna noae

Previously confused with the small giant clam Tridacna maxima, the recently resurrected Noah’s giant clam, Tridacna noae, has been reported from the Taiwanese and the Ryukyu archipelagoes. Our recent underwater observations now extend its distribution to Dongsha (northern South China Sea), Bunaken (Sulawesi Sea), Madang and Kavieng (Bismarck Sea), the Alor archipelago (Sawu Sea), Kosrae (Caroline Islands), New Caledonia, the Loyalty Islands and Vanuatu (Coral Sea), Viti-Levu (Fiji), Wallis Island, and Kiritimati (Northern Line Islands). Published mitochondrial DNA sequences retrieved from open-access databases also indicate its presence in eastern Negros (Philippines), in the Molucca Sea, at Ningaloo Reef (Western Australia), and in the Solomon Islands. Noah’s giant clam is thus a widely distributed Indo-West Pacific species. Wherever research has been done on small giant clams throughout T. noae’s range, the inadvertent confusion of T. noae with T. maxima might have led to overestimating actual T. maxima densities and to errors in estimating demographic parameters.

Discrete and continuous reproductive tactics in a hermaphroditic society

An important step towards understanding conflicts in animal societies lies in identifying socioecological predictors of individual reproductive tactics. In gonochoristic species, individuals can choose to adopt breeding or nonbreeding tactics, and if they breed, how large a share of reproduction they acquire. In hermaphroditic species, individuals can also adopt male or female breeding tactics. Hermaphrodites’ wider suite of reproductive options makes them interesting models for investigating predictors of reproductive tactics. We used molecular and ecological data to determine socioecological correlates of discrete (breeding versus nonbreeding; males versus female) and continuous (share of reproduction) reproductive tactics in the hermaphroditic coral-dwelling fish, Dascyllus aruanus. The number of potential competitors within groups was positively related to coral size, and the amount of total reproduction over which they competed was associated with the size of the largest individual (i.e. the parental male). Discrete and continuous reproductive tactics were strongly influenced by rank and body size: high-ranking and large individuals were more likely to breed and attain larger reproductive shares and output. High-ranking breeders also obtained a larger reproductive output if they adopted male tactics, whereas low-ranking breeders obtained a larger share if they adopted female tactics, which can explain why these fish show protogynous sex change. Genetic analysis also revealed that subordinates could attain a larger reproductive share than dominants, and that extragroup individuals could contribute to reproduction. Our results shed new light on the causes of variation in reproductive tactics, the payoffs from group membership and the nature conflict in hermaphroditic societies.

Isolation and characterization of 16 microsatellite loci in the humbug damselfish, Dascyllus aruanus (family Pomacentridae)

Here we report on 16 microsatellite loci designed for the damselfish Dascyllus aruanus. All loci were tested on 98 individuals and were polymorphic (seven to 35 alleles). Expected heterozygosity ranged from 0.705 to 0.942. Six loci showed Hardy‐Weinberg disequilibrium due to the occurrence of null alleles. Cross‐species amplifications conducted within the genus Dascyllus (D. carneus, D. strasburgi, D. trimaculatus) lead to polymorphic fragments in 32 out of 48 tests. These 16 loci will enable future research into the behavioural ecology and population ecology of Dascyllus aruanus throughout the Indo‐Pacific.

Unexpected high densities of the hybrid coral Acropora prolifera (Lamarck 1816) in Guadeloupe Island, Lesser Antilles

Since the 1980s, coral populations of Acropora palmata (Lamarck 1816) and A. cervicornis (Lamarck 1816) have dramatically declined in the Caribbean and have been consequently classified as critically endangered since 2008 (IUCN). Acropora palmata and A. cervicornis can form a viable F1 offspring previously described as A. prolifera by Lamarck (Vollmer and Palumbi 2002). Few isolated colonies of that morphotype have punctually been reported on Lesser Antilles reefs in the previous decades. In January 2013, high densities of morphologically identified A. prolifera colonies were observed in the Bay of Grand Cul-de-Sac Marin (16 21¢24.19†N; 61 35¢35.12†W, Guadeloupe Island, Lesser Antilles), whereas no colonies were found at this exact same site prospected in May 2011 (Fig. 1). Genetic microsatellite analyses (unpublished data) verified the hybrid nature of the colonies and suggest that they may constitute a single clone. However, in other Caribbean sites, Fogarty (2010) found high genotypic diversity for that hybrid. As a consequence of decreased parental species’ density, eggs likely float unfertilized, increasing the probability of heterospecific sperm encounters and thus hybrid embryo formation (Fogarty et al. 2012).

Isolation and characterization of fifteen microsatellite loci for the giant clam Tridacna maxima

Fifteen polymorphic microsatellite markers were developed for Tridacna maxima in order to assess self-recruitment and larval dispersal within and among MPAs in New Caledonia and provide baseline data for conservation management of this species. Number of alleles varied from 5 to 25 per locus, observed and expected heterozygosities ranged from 0.171 to 0.860 and 0.591 to 0.935 respectively. Significant deviations from HWE were detected in eight loci. Cross-amplifications were tested in five other species of Tridacnidae (T. crocea, T. squamosa, T. derasa, T. noae and Hippopus hippopus).

Significance of new records of Tridacna squamosa Lamarck, 1819, in the Tuamotu and Gambier Archipelagos (French Polynesia)

The giant clam subfamily Tridacninae (family Cardiidae) is an important group of bivalve molluscs found throughout the Red Sea and Indo-Pacific, from East Africa to the Eastern Pacific biogeographic region. The Tridacna genus is currently revised with numerous cryptic species identified with molecular markers. New Tridacna records from the fringe of the known distribution areas are extremely useful to identify genetically unique species, geographic ranges, and to examine processes associated with species differentiation. While Tridacna maxima is abundant in French Polynesia (Central South Pacific Ocean) the larger fluted giant clam Tridacna squamosa was formerly reported only in the Austral Islands in the south. Following a recent survey that spanned 23 islands and atolls of the Society, Tuamotu and Gambier Archipelagos, the presence of T. squamosa between the Cook Islands and Pitcairn Islands is confirmed using both morphological and molecular information, suggesting a relic distribution across the Central Pacific Ocean. Tridacna squamosa is rare, but present throughout Tuamotu and Gambier. However, it remained undetected from the Society Islands, probably due to historical over-fishing. This species is valued by local inhabitants, and is sought after mainly as gifts and also for a limited local shell trade. The rarity of T. squamosa may call for conservation measures in the near future.

Isolation and characterization of fifteen microsatellite loci for the giant clam Hippopus hippopus (family Tridacnidae)

Fifteen polymorphic microsatellite markers were developed for Hippopus hippopus in order to assess the effectiveness of population replenishment within marine protected areas in New Caledonia. Number of alleles varied from 2 to 11 per locus, observed and expected heterozygosities ranged from 0.300 to 0.866 and 0.495 to 0.858 respectively. Significant deviations from HWE were detected in two loci. Cross-amplifications were tested in four other species of Tridacnidae.

First record of the Devil Clam, Tridacna mbalavuana Ladd 1934, in New Caledonia

The Devil Clam, Tridacna mbalavuana Ladd 1934, previously known as T. tevoroa Lucas, Ledua, Braley 1990, was described on the barrier reefs of Tonga and the Lau islands of Fiji. Here, we report two individuals found on the northeastern barrier reef of New Caledonia. While its known geographic range has expanded, its rarity and hence vulnerability persists.

Considering reefscape configuration and composition in biophysical models advance seascape genetics

Previous seascape genetics studies have emphasized the role of ocean currents and geographic distances to explain the genetic structure of marine species, but the role of benthic habitat has been more rarely considered. Here, we compared the population genetic structure observed in West Pacific giant clam populations against model simulations that accounted habitat composition and configuration, geographical distance, and oceanic currents. Dispersal determined by geographical distance provided a modelled genetic structure in better agreement with the observations than dispersal by oceanic currents, possibly due to insufficient spatial resolution of available oceanographic and coastal circulation models. Considering both habitat composition and configuration significantly improved the match between simulated and observed genetic structures. This study emphasizes the importance of a reefscape genetics approach to population ecology, evolution and conservation in the sea.