Reproductive behavior of intersexes of an intertidal amphipod Corophium volutator

Abstract. Intersexes are common in crustaceans. Typically, these intersexes are sterile or function as females, but prior evidence from laboratory experiments suggests that intersexes of a key species of gammaridean amphipod, Corophium volutator , might function as males. We observed that intersexes of C. volutator behaved as males by crawling (mate-searching) on a mudflat during ebb tides and pairing in burrows with female amphipods. In the laboratory, intersexes and males did not differ in aspects of crawling such as movement rate and measures of burrow investigation. I`ntersexuality was costly in that intersexes crawled less often than males on a mudflat, formed fewer pairs with females than males, and remained in tandem less often with receptive females than males. The use of PCR-based identification methods failed to identify the presence of transovarial, feminizing, microsporidian parasites as a major cause of intersexuality in this species in that infected females did not produce broods that contained more intersexes than broods produced by uninfected females. Because intersexes may be mistaken as females, the percentage of functional males in amphipod populations may be underestimated: an important consideration given male limitation in populations of C. volutator. The occurrence of intersexes has significant implications for studies on the evolution and ecology of sex ratios, and the use of crustaceans as indicators of environmental quality.     

Biomechanics and energy cost of the amphipod Corophium volutator filter-pump

The integrated function of the setal filter-basket and the pleopodal pump in the burrowing amphipod Corophium volutator was studied by video-microscopy in order to evaluate the energy costs of filter feeding. Video-microscope observations indicated that, in general, nine short, water-pumping beat cycles of the pleopods are succeeded by one slow cycle that coincides with cleaning of the setal filter and transient slowdown of inhalant water velocity. The position of the plumose setal filter on the second pair of gnathopods ensures that all water runs through the filter-basket. The fine V-shaped bristles on the setae enlarge the total filter area so that the velocity of water flowing through the filter is relatively slow, about 2.5 mm s(-1), giving rise to a resistance of about 2.9 mm H(2)O, which is the most important contribution to the total pressure drop in the system. In "standard" individuals of C. volutator with lengths of 3 and 6 mm, the normal operating pump pressure and pumping rate were, respectively, 2.6 and 3.1 mm H(2)O, and 18.3 and 85.5 ml h(-1); the overall pump efficiencies were 5.1% and 11.6%, respectively. These results show that the Corophium filter-pump is comparable to other low-pressure biological pumps in filter-feeding marine invertebrates, such as mussels, polychaetes, ascidians, and bryozoans.     

Surface deposit feeding versus filter feeding in the amphipod Corophium volutator

The previously indicated ability of the amphipod Corophium volutator to switch between deposit feeding and filter feeding was confirmed and studied in more detail in controlled laboratory experiments in which filtration rate measurements were combined with simultaneous video recordings of surface-feeding activity of the amphipod exposed to different known concentrations of algal (Tetraselmis sp.) cells. When algal cells were added to the ambient water, this stimulated C. volutator, buried in natural sediment or transferred to glass tubes, to commence filter feeding, which was maintained as long as the algal concentration was kept above a certain threshold level. However, shortly after the algal concentration was grazed below the threshold level, filter feeding was abandoned and replaced by surface deposit feeding, as evident from a video observed increase in surface scraping frequency. The average frequency of surface scraping was 0.64±0.27 min^-1, with a residence time of 3.7±1.4 s on the sediment surface where the amphipod grabbed material within a semicircle. Such detailed knowledge of filter feeding versus deposit feeding in C. volutator is of importance for a better understanding of the ecological role of this key organism in many shallow-water ecosystems where the feeding conditions are frequently changing.     

Parasites on an intertidal Corophium-bed: factors determining the phenology of microphallid trematodes in the intermediate host populations of the mud-snail Hydrobia ulvae and the amphipod Corophium volutator

The phenology of microphallid trematodes within their intermediate hostpopulations has been studied on an intertidal mud flat. The parasites usethe mud snail Hydrobia ulvae and the infaunal amphipod Corophium volutatoras first and secondary intermediate host, respectively. Migratory shorebirdsact as final hosts. Our results show a general trend of decline in thedensity of infected intermediate hosts during both spring and autumn, whichcould mainly be ascribed to shorebird predation. During summer the densityof both infected snails and infected amphipods increased considerably, witha culmination in June within the snail population (1000 infectedm-² and in August within the amphipod population (40 000infected m-². This time lag in parasite occurrence could berelated to (1) the development time of larval trematodes within the snails,(2) higher ambient temperatures in late summer increasing parasitetransmission between snails and amphipods during this period, and (3) ageneral increase in the Corophium population during late summer. Fromsamples collected between 1990 and 1995 it is shown that microphallidtrematodes occasionally may give rise to mass mortality in the amphipodpopulation. The prerequisites for such an event are a high parasiteprevalence within the first intermediate host population and unusually highambient temperatures, facilitating parasite transmission to the secondaryintermediate host, C. volutator.     

Genetic isolation of populations of the gammaridean amphipod, Corophium volutator, in the Bay of Fundy, Canada

Selection experiments suggest that evolutionary modifications in amphipod demography can respond to local environmental changes and that local races of amphipods may be common. We tested this hypothesis in mudflat populations of Corophium volutator in the Bay of Fundy, Canada. Due to the unique topography of the Bay of Fundy, distinctive environmental conditions are prevalent in different branches of the Bay, while the impact of shorebird predation has also been shown to vary between populations. Several hypotheses have been suggested to explain ecological evidence which indicates that Corophium volutator (Pallas), a common amphipod crustacean, exhibits extensive life history variation in Bay of Fundy populations. We used RAPD-PCR techniques to examine populations of C. volutator in an investigation of genetic isolation in marine environments. Our data suggest that variation in selection pressures have played a significant role in the genetic divergence of populations of C. volutator in the Bay of Fundy.     

The influence of Corophium volutator abundance on resuspension

Two experiments were performed to test the hypothesis that Corophium volutator affects the turbidity of water in estuaries through active resuspension of sediment. One experiment was done in a flume system under different flow velocities, and one in aquaria. A diatom film developed at the sediment surface in both experiments before Corophium was added. This diatom film was supposed to have a stabilising effect on the sediment. In both experiments, the concentration of suspended solids in the water column increased with the density of Corophium individuals. No effect of flow velocity on suspended solids concentration was found. This indicates that, in our flume experiment, active resuspension by Corophium was more important than physical resuspension, at least at low flow velocity (<20 cm s^-1) and in the presence of a diatom film. The critical erosion threshold decreased with increasing Corophium density in the aquarium experiment, indicating that indirect effects of Corophium grazing may become more important at high levels of bottom shear stress. The implications of our findings for suspended solids concentration in estuarine systems are discussed.     

Functional morphology of the stomach of Corophium volutator Pallas

Corophium volutator Pallas is a small amphipod crustacean which burrows in inter-tidal mud on the British coast, and feeds on organic detritus, mainly vegetable, by selecting particles from the mud.
The alimentary canal consists of foregut, midgut and hindgut. The midgut is produced into a pair of anterior dorsal caeca, a pair of ventral caeca and a pair of posterior dorsal caeca.
The cardiac stomach has a large number of chitinous plates or ridges beset with hooks and spines for the trituration of food.
The pyloric stomach has long fine bristles which form an eifective filter apparatus and allow only fine particles of food to pass into the midgut, where they are digested and absorbed.
The hepato-pancreas secrete digestive enzymes and store reserve food material as oil globules.     

The behaviour of Corophium volutator (Crustacea: Amphipoda)

The behaviour of Corophium volutator (Pallas) is outlined. Swimming, crawling, burrowing and feeding activities are described in detail. Animals usually swim on their backs. Every few seconds, swimming alternates with passive sinking. Animals can crawl over surfaces in and out of water. Out of water they do so by a looping motion using their second antennae and telson. When out of water animals crawl away from light and down slopes. In water they swim towards light. Burrowing is initiated by rapid beating of the pleopods; the animal then sinks below the surface by a concerted action of pereiopods, pleopods, telson, uropods and second antennae; within a few minutes, a shallow burrow is formed. The formation of permanent burrows is dependant on particle size, on adhesive properties of detritus and primary films on sand particles, and on a secretion produced by the animal itself. Individuals can turn about in permanent burrows. The species is essentially a detritus feeder. Animals normally feed only when in their burrows, by using their second antennae to scrape material from the substrate surface into the entrance of the burrow. This material is then transported to the mouth by the feeding appendages and respiratory current. The behaviour of small and large animals differs; small animals burrow rapidly and permanently, and do not emerge spontaneously; furthermore, they only swim occasionally. Large animals swim more frequently, spend more time on the substrate surface, and periodically move burrows. It is suggested that new habitats are colonized by large animals which have already bred once.     

Behavioral Response of Corophium volutator to Shorebird Predation in the Upper Bay of Fundy,Canada

Predator avoidance is an important component of predator-prey relationships and can affect prey availability for foraging animals. Each summer, the burrow-dwelling amphipod Corophium volutator is heavily preyed upon by Semipalmated Sandpipers (Calidris pusilla) on mudflats in the upper Bay of Fundy, Canada. We conducted three complementary studies to determine if adult C. volutator exhibit predator avoidance behavior in the presence of sandpipers. In a field experiment, we monitored vertical distribution of C. volutator adults in bird exclosures and adjacent control plots before sandpipers arrived and during their stopover. We also made polymer resin casts of C. volutator burrows in the field throughout the summer. Finally, we simulated shorebird pecking in a lab experiment and observed C. volutator behavior in their burrows. C. volutator adults were generally distributed deeper in the sediment later in the summer (after sandpipers arrived). In August, this response was detectably stronger in areas exposed to bird predation than in bird exclosures. During peak predator abundance, many C. volutator adults were beyond the reach of feeding sandpipers (>1.5 cm deep). However, burrow depth did not change significantly throughout the summer. Detailed behavioral observations indicated that C. volutator spent more time at the bottom of their burrow when exposed to a simulated predator compared to controls. This observed redistribution suggests that C. volutator adults move deeper into their burrows as an anti-predator response to the presence of sandpipers. This work has implications for predators that feed on burrow-dwelling invertebrates in soft-sediment ecosystems, as density may not accurately estimate prey availability.     

Tube-building in two epifaunal amphipod species,Corophium insidiosum andJassa falcata

Jassa falcata andCorophium insidiosum are epifaunal tube-building marine amphipods, whose niches overlap in habitat and food requirements. Laboratory experiments were conducted to study the influence of the quality of different available particulate substrates on settlement and tube-building behaviour of these two amphipod species. Our experiments suggest thatC. insidiosum is less specialized in this respect thanJ. falcata. C. insidiosum is able to use organic materials for tube-building such as artificial (Ulva spec. powder) or mixed natural detritus as well as inorganic material (coarse sand); whereasJ. falcata utilizes organic materials, but sand only to a very limited extent.     

Reproductive synchrony in captive macaques

Captive bonnet macaques housed at the California Primate Research Center reproduce seasonally. The chances of producing surviving infants were substantially reduced among females who conceived at the peak of the mating season compared with females whose conceptions were more isolated in time. Primiparous females and low ranking females were most consistently affected by the extent of reproductive synchrony. Behavioral data suggest that harassment of conceiving and pregnant females may have contributed to the correlation between the extent of reproductive synchrony and infant mortality as the levels of aggression toward females were highest during the months in which conceptions were most common.     

Behaviour and time allocation of the mud shrimp, Corophium volutator, during the tidal cycle: a laboratory study

Despite the numerous ecological and behavioural studies, relatively little is known about the behavioural dynamics of Corophium volutator during the tidal cycle. In the present study, the behaviour of C. volutator was observed in the laboratory in a tide-simulated aquarium, and time allocation of the different activities was quantified. Overall, the surface activity was low and showed a steep decline after submersion. A clear tide-based cyclic pattern was found, with a boost of activity immediately after first submersion, continuing during submersion, and shifting over a period with decreasing activity towards almost total inactivity at the end of emersion.     

Anthropocene invasion of an ecosystem engineer: resolving the history of Corophium volutator (Amphipoda: Corophiidae) in the North Atlantic

Resolving the natural histories of species is important for the interpretation of ecological patterns, as it provides evolutionary context for the interactions between organisms and their environment. Despite playing an integral role on the intertidal mudflats of the North Atlantic as an abundant food source for predators and as an ecosystem engineer that alters the soft sediment environment, no previous studies have provided empirical evidence to determine the biogeographical origin of the amphipod Corophium volutator. To resolve its status as introduced or indigenous in Europe and North America, we analyzed sequence data for two mitochondrial loci and two nuclear markers, aiming to determine whether the present range of C. volutator is the result of unresolved taxonomy, persistence in glacial refugia, natural trans‐Atlantic dispersal, or human‐mediated introduction. Our results demonstrate a reduced genetic diversity in North American populations that is a subsample of diversity in European populations, with coalescent analyses of mitochondrial and nuclear DNA supporting different models of multiple introductions from Europe to the Bay of Fundy and Gulf of Maine in North America. These results suggest that C. volutator was introduced to North America prior to the first surveys of local biota in the 20th Century, which has broad implications for interpretations of community and ecosystem interactions in the North Atlantic intertidal. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 288–304.     

A laboratory-based comparison of osmoregulatory ability at different water temperatures and salinities in the stenothermic isopod Saduria entomon (Linnaeus, 1758) and the eurythermic amphipod Corophium volutator (Pallas, 1766) from the Baltic Sea

The aim of the investigation was a comparison of osmoregulatory ability at different water temperatures and salinities by the stenothermic isopod Saduria entomon (Linnaeus, 1758) and the eurythermic amphipod Corophium volutator (Pallas, 1766) from the Baltic Sea. The experiments were performed under laboratory conditions at different water temperatures (5, 10 and 15?°C) and salinities (3, 6.6, 15 and 25 PSU for S. entomon and 3, 6.3, 15 and 25 PSU for C. volutator). The osmotic concentrations of the crustaceans’ haemolymph were determined using the melting point method. Temperature had a statistically significant effect on the osmoregulation in S. entomon, but had generally no statistical influence on the osmoregulation in C. volutator. This physiological information regarding adaptation provides a basis for predicting the distribution of these species in changing environments. The implications of the results for the comparative adaptability of the two species are considered.     

Laboratory Studies of Parasite Transmission Aspects between Hydrobia spp. (Gastropoda) and Corophium volutator (Amphipoda)

Aspects of parasite transmission between Hydrobia spp. and Corophium volutator, first and second intermediate host of digenetic trematodes, were investigated under laboratory conditions. H. ventrosa is used as an intermediate host by several trematode species. Under laboratory conditions the most frequently observed emergence from H. ventrosa was of cercariae of Maritrema subdolum. The number of cercariae shed per day varied considerably. It was observed that 30 cercariae on average and up to 450 cercariae at maximum can emerge from a single H. ventrosa per day. Cercarial production continued until the death of the snails. The life-span of cercariae of the species M. subdolum decreased as the water temperature increased. It can be concluded that under natural conditions the cercariae, after emerging, have a maximum period of 1 day in which to seek out their second intermediate host C. volutator. Almost all specimens of C. volutator exposed to cercariae of the species M. subdolum died within the test period of 6 days. High average cercarial densities caused short life-spans (<50 h), while at lower densities longer survival times were possible. For cercariae of other Trematoda species, we were unable to find any equally clear evidence of a reduction in the survival rate of C. volutator within the test period. Mortality of C volutator, and other effects of infestation, as observed in our experiment, can be assumed to be a result of the penetration process of the cercariae but they also can be attributed to the mesocercariae.     

Reproductive synchrony in a recovering bottlenecked sea turtle population

1. The assessment of species extinction risk has been well established for some time now. Assessing the potential for recovery in endangered species is however much more challenging, because complementary approaches are required to detect reliable signals of positive trends. 2. This study combines genetics, demography and behavioural data at three different time-scales to assess historical and recent population changes and evidence of reproductive synchrony in a small population of olive ridley sea turtle Lepidochelys olivacea. Lepidochelys is considered as the most extraordinary example of reproductive synchrony in reptiles, yet to date, it has only been reported in large populations. 3. Using Bayesian coalescent-based models on microsatellite nuclear DNA variability, we demonstrate that effective population size in olive ridleys nesting in French Guiana has dramatically declined by 99% over the last 20 centuries. This low current population size is further illustrated by the absence of genetic mitochondrial DNA diversity in the present nesting population. Yet, monitoring of nesting sites in French Guiana suggests a possible recovery of the population over the last decade. 4. Satellite telemetry shows that over the first 14 days of their 28-days inter-nesting interval, i.e. when eggs maturation is likely to occur, gravid females disperse over the continental shelf. They then gather together with a striking spatiotemporal consistency close to the nesting site, where they later emerge for their second nesting event. 5. Our results therefore suggest that reproductive synchrony also occurs in small populations. Olive ridleys may ensure this synchrony by adjusting the duration of the second half of their inter-nesting interval prior to landing, possibly through social mediation. 6. Such reproductive synchrony may be related to the maintenance of some species-specific strategy despite former collapse and may contribute to the present population recovery. The gregarious behaviour of reproductive individuals close to shore where human-induced perturbations occur is however a cause for conservation concern for this still poorly known species.     

Reproductive biology of the rosylip sculpin, an intertidal spawner

Rosylip sculpin Ascelichthys rhodorus spawned in the intertidal during the winter in the north‐eastern Pacific. Large numbers of males typically congregated at spawning sites, where females deposited clutches. The mating system of this species was external fertilization and group spawning at specific oviposition sites under boulders in the intertidal, and no alternative male mating strategies. Males were abundant at sites while oviposition was occurring, and most abandoned the sites as spawning tapered off seasonally despite the presence of developing clutches. Experimental removal of males from sites suggested that males provided some short‐term benefits to clutches, with catastrophic loss of clutches significantly lower when males were present. The large number of males at an oviposition site and histological evidence indicating high sperm production and storage of sperm prior to release suggest a high level of sperm competition in this species. This spawning pattern appears to differ in substantial ways from any other reported fish mating system.     

Reproductive competition and the evolution of extreme birth synchrony in a cooperative mammal

Reproductive events in animal societies often show a high degree of temporal clustering, but the evolutionary causes of this synchronization are poorly understood. Here, we suggest that selection to avoid the negative effects of competition with other females has given rise to a remarkable degree of birth synchrony in the communal-breeding banded mongoose (Mungos mungo). Within banded mongoose groups, births are highly synchronous, with 64 per cent of females giving birth on exactly the same night. Our results indicate that this extreme synchrony arises because offspring suffer an increased risk of infanticide if their mother gives birth before other females, but suffer in competition with older littermates if their mother gives birth after them. These findings highlight the important influence that reproductive competition can have for the evolution of reproductive synchrony.