Sara Fratini

Genetic differentiation in the mud crab Scylla serrata (Decapoda: Portunidae) within the Indian Ocean

Scylla serrata (Decapoda: Portunidae) is a swimming crab that is widespread in the Indo-Pacific region and commonly found in estuarine and mangrove waters. An extended planktonic larval phase suggests high dispersal potential and the possibility of extensive gene flow between conspecific populations at least on a geographic mesoscale (tens to hundreds of kilometres). Intraspecific variation of the mitochondrial DNA cytochrome oxidase subunit I (mtDNA COI) gene was investigated in 77 individuals from four representative mangrove swamps of the African tropics (Kenya and Zanzibar) by means of DNA sequencing. We examined 535 base pairs (bp) and identified 24 different haplotypes. Each population sample is characterised by a single most frequent haplotype, shared among all four populations, and a small number of rare ones, typically present in only one or two individuals and representative of a specific population. Analysis of molecular variance (AMOVA), FST statistics and χ2 contingency analysis of spatial distribution of mtDNA haplotype frequencies revealed in toto a significant genetic differentiation among populations. These results could indicate that gene flow might be reduced, even between geographically close sites, despite the high potential for dispersal; anyway, at the recorded level of divergence and owing to the abundance of rare haplotypes and singletons in our data set, repeated sampling over time is necessary to establish whether the recorded pattern of genetic differentiation is stable and biologically significant. Finally, integration of our data with those reported by Gopurenko et al. [Mar. Biol. 134 (1999) 227] on S. serrata from South Africa, Red Sea and Mauritius Islands allowed to infer S. serrata population structure within a larger area of the Indian Ocean region.

Behavioural evidence for the involvement of Dufour's gland secretion in nestmate recognition in the social wasp Polistes dominulus (Hymenoptera : Vespidae)

Abstract The results of recent studies by our group have suggested that in social wasps of the genus Polistes the Dufour’s gland is involved in kin recognition. In fact, the same hydrocarbons occurring on the cuticle are found in the gland secretion, and in P. dominulus the composition of the glandular secretion is more similar in foundresses belonging to the same colonies than in heterocolonial foundresses. In this study, P. dominulus colonies were experimentally presented with previously treated dead conspecific females. These lures had been deprived of their epicuticular lipids and coated with epicuticular or Dufour’s gland secretion extracts from females hetero- or homocolonial with respect to the tested colonies. The behaviour of the colonies towards these lures indicates that, like the epicuticular lipids, the Dufour’s gland secretion is involved in nestmate recognition.

Phylogenetic and morphometric differentiation reveal geographic radiation and pseudo-cryptic speciation in a mangrove crab from the Indo-West Pacific

The presence of boundaries to dispersal has been recently documented for many Indo-West Pacific (IWP) species with planktonic propagules and a widespread distribution. We studied the phylogeography of the mangrove crab Neosarmatium meinerti (Brachyura: Sesarmidae) and the phylogenetic relationship to its presumed sister species N. fourmanoiri in the IWP in order to compare intraspecific with interspecific diversity. Portions of the mitochondrial genes 16S and CoxI were sequenced for 23 specimens of N. meinerti and 5 N. fourmanoiri, while a fragment of the 28S was obtained for a subset of specimens. Genetic data are supplemented by morphometric and based on 37 adult males of N. meinerti and 9 males of N. fourmanoiri. The conserved nuclear 28S reveals the existence of a genetic break between the Indian and Pacific oceans. Otherwise, mitochondrial genes as well as morphometry clearly support the presence of a species complex within N. meinerti composed by four well structured and geographically defined lineages: East African coast; western Indian Ocean islands; South East Asia; and Australia.

Feeding clusters and olfaction in the mangrove snail Terebralia palustris (Linnaeus) (Potamididae : Gastropoda)

Large numbers of the snail Terebralia palustris (Linnaeus) (Potamididae; Gastropoda) are frequently observed feeding in a cluster on a single fallen mangrove leaf, yet none are present on leaves nearby. Consequently, we investigated the food-finding ability of T. palustris in a Kenyan mangrove forest using field experiments. We estimated the attractive effect of different cues and analysed the paths (video-recorded) of snails when approaching a food-related odour. This intertidal snail can potentially use both air-borne and water-borne odours to locate food. T. palustris is attracted to conspecifics feeding on leaves, while intact leaves as well as non-feeding snails are not attractive. Moreover, the guiding stimulus appears to be compounds released when the leaves are damaged.T. palustris also seems able to discriminate between different food items; it is more strongly attracted to green mangrove leaves than senescent or fallen ones or mangrove propagules, probably because green leaves release a greater amount of attractive cues.Feeding snails thus recruit more snails to feed on the same leaf. The ecological implications of this behaviour are discussed: a large number of snails on the same leaf counteracts the ability of crabs to remove the leaf being eaten by the snails.

Tree-climbing behaviour of Cerithidea decollata , a western Indian Ocean mangrove gastropod (Mollusca: Potamididae)

The behaviour of Cerithidea decollata , a common western Indian Ocean mangrove tree climbing gastropod, was studied in Mida Creek, Kenya. At the study site, this snail mainly lived in Avicennia marina dominated areas, i.e. in the mangrove belt between high water spring tide and high water neap tide levels. Not a single individual was found on the less common mangrove tree Lumnitzera racemosa , living just above the A. marina level (together with terrestrial grass), and was very rarely recorded on the common Rhizophora mucronata , bordering the seaward side of the A. marina belt. No significant gradient of C. decollata density was found within the whole 150–200 m wide belt. The majority of C. decollata rested on tree trunks during high tide, creeping on the mud flat below the tree for part of low tide, and returning on the trunks well before being reached by the water. This migratory pattern was more evident at spring than at neap tide, at day than at night time and it was strongly influenced by the shore level of the mangrove zone in which animals resided. While C. decollata from lower shore levels neatly massively migrated twice a day, individuals from upper levels showed a more continuous and irregular activity, sometimes crawling on the mud even at high water of spring tide, when they experience just a few centimetres of water for no more than one to two hours.

FEEDING, TEMPORAL, AND SPATIAL PREFERENCES OF METOPOGRAPSUS THUKUHAR (DECAPODA; GRAPSIDAE): AN OPPORTUNISTIC MANGROVE DWELLER

Abstract Metopograpsus thukuhar is a very common grapsid in the Indo-Pacific mangroves but is found only occasionally in a non-mangrove environment. Field observations investigated its spatial and temporal strategies and clarified its predatory abilities. Gut-content analysis was used to assess its natural diet. Metopograpsus thukuhar was mainly active during low tide, although many crabs were seen at high tide moving on the mangrove roots above the water level. It lived largely among the roots of the seaward Rhizophora mucronata and concentrated its activity within a definite area of the root apparatus of a single tree, appearing to be faithful to one or two specific crevices. The diet of M. thukuhar was principally based on macroalgae; mangrove leaves were also present, but animal items were rare. However, direct field observations of the crabs predatory behavior indicate that this grapsid is an opportunistic feeder with a certain degree of behavioral plasticity.

Prey selection of epixanthus dentatus (Crustacea: Brachyura: Eriphiidae) as determined by its prey remains

Epixanthus dentatus (Crustacea: Brachyura: Eriphiidae) is a predator crab, commonly inhabiting East African mangroves, whose nocturnal and elusive behaviour usually prevents analysis of its natural diet and prey selection. The present study was carried out on a population inhabiting a peculiar mangrove habitat in which E. dentatus produces heaps of non-ingested parts of its prey. Fifty-nine of these accumulations of prey remains were examined and 17 species were identified as part of the diet of E. dentatus . Relative prey consumption was then analysed with respect to the relative abundance of prey species within the local faunal community. This methodology provided important information about prey selection by E. dentatus ; in particular, gastropods were always strongly under-represented, while there was an active selection among the different crab species. Uca species were under-represented, while swimming crabs were also part of the E. dentatus diet, which shows that the latter is able to prey both at low and high tide.

Competition for mangrove leaf litter between two East African crabs, Neosarmatium meinerti (Sesarmidae) and Cardisoma carnifex (Gecarcinidae): a case of kleptoparasitism?

Many Indo-Pacific mangrove macroinvertebrates are herbivorous and heavily dependent on leaf litter. As a consequence, fallen leaves become a limiting factor and competition occurs among conspecifics and heterospecifics. Neosarmatium meinerti and Cardisoma carnifex are two of the most common herbivorous crabs of the landward mangrove belt in East Africa, often sharing an area and time of activity. This study used a series of field experiments to investigate their feeding habits when co-existing. The high density reached by both species led to overlapping of the individual feeding ranges: during the feeding excursions each crab inevitably encountered, and actively interacted with, other conspecifics and heterospecifics. Competition for food was high: N. meinerti lost approximately 50% of its leaves to theft by C. carnifex. Thus, approximately half of the leaves obtained by C. carnifex were stolen from a foraging N. meinerti. Considering the frequency of such thefts, C. carnifex may be regarded as a facultative kleptoparasitic species. This is the first time that a such strategy has been recorded for a crab species and for a vegetable resource.

Demographic History and Reproductive Output Correlates with Intraspecific Genetic Variation in Seven Species of Indo-Pacific Mangrove Crabs.

The spatial distribution and the amount of intraspecific genetic variation of marine organisms are strongly influenced by many biotic and abiotic factors. Comparing biological and genetic data characterizing species living in the same habitat can help to elucidate the processes driving these variation patterns. Here, we present a comparative multispecies population genetic study on seven mangrove crabs co-occurring in the West Indian Ocean characterized by planktotrophic larvae with similar pelagic larval duration. Our main aim was to investigate whether a suite of biological, behavioural and ecological traits could affect genetic diversities of the study species in combination with historical demographic parameters. As possible current explanatory factors, we used the intertidal micro-habitat colonised by adult populations, various parameters of individual and population fecundity, and the timing of larval release. As the genetic marker, we used partial sequences of cytochrome oxidase subunit I gene. Genetic and ecological data were collected by the authors and/or gathered from primary literature. Permutational multiple regression models and ANOVA tests showed that species density and their reproductive output in combination with historical demographic parameters could explain the intraspecific genetic variation indexes across the seven species. In particular, species producing consistently less eggs per spawning event showed higher values of haplotype diversity. Moreover, Tajima’s D parameters well explained the recorded values for haplotype diversity and average γst. We concluded that current intraspecific gene diversities in crabs inhabiting mangrove forests were affected by population fecundity as well as past demographic history. The results were also discussed in terms of management and conservation of fauna in the Western Indian Ocean mangroves.

Establishing the eradication unit of Molara Island: a case of study from Sardinia, Italy.

Molara is a small island belonging to the Marine protected Area Tavolara—Punta Coda Cavallo, in Sardinia. During 2006–2007, a bio-monitoring program reported a strong presence of the black rat, Rattus rattus, on Molara island. Rat predation has detrimentally affected the unique biodiversity of this island, thus, in 2008 an eradication campaign was conducted. Our eradication protocol included a pre-eradication genetic investigation, using 8 microsatellite loci, on a rat population of Molara as well as on neighbour islands within the Marine Protected Area (MPA). The main goal of this genetic investigation was to establish the correct borders of the eradication unit of Molara island. As several recent eradication campaigns have been unsuccessful, due to incomplete and unstable eradication, we also aimed to assess possible hidden sources of reinvasion. Specimens were also collected during post- eradication monitoring on Molara for genetic screening to establish their origin, and thus validate the effectiveness of our eradication campaign. According to our genetic analysis, within the MPA there are four different eradication units, corresponding to the islands of Molara, Tavolara, Piana and to the Sardinia mainland. Gene flow among these four units is more or less absent. The assignment and clustering tests performed on pre and post-eradication samples seem to indicate that the population of Sardinia mainland is a possible source of re-invasion for the Piana and Molara populations.