Molt cycle alterations in behavior,feeding and diel rhythms of a decapod crustacean,the spiny lobster Panulirus argus

The crustacean molt cycle manifests extensive behavioral changes in addition to physiological and integumentary modifications. The paucity of quantitative studies led us to characterize molt stage dependent alterations in rhythmic locomotor, feeding, and agonistic behavior of subadult spiny lobster Panulirus argus held grouped and solitarily in simulated natural conditions. Non-disruptively determined molt stages were defined as proportions of intermolt duration. Significant nocturnal rhythmicity persisted through the full molt cycle, though daily form varied as a function of activity level and molt stage. A distinct early evening peak signaled initiation of foraging and walking behavior. Thereafter, rhythm amplitude either declined progressively (low activity: unimodal pattern), remained high (high activity: nocturnal plateau), or exhibited a secondary early morning peak (intermediate activity: bimodal and polymodal patterns). Activity ceased at or immediately prior to sunrise. Ecdysis was predominantly nocturnal, probably reflecting species specific spatiotemporal movement patterns and social behavior. A selective advantage of nocturnal ecdysis was postulated concerning avoidance of cannibalism and diurnal predators. Locomotor activity and feeding rates were not equivalent through the molt cycle, though both peaked in stages B₂-C₁. Locomotor activity remained high in metecdysis, decreased sharply at proecdysis initiation (D₀), reaching lowest levels in D₁-D₃, then increased in D₃ through B₁. Activity dropped steeply at ecdysis, though lobsters were capable of intense and coordinated activity. Feeding decreased slowly through metecdysis after the B₂-C₁ maximum, then increased temporarily in C₄ and D₀, indicating heightened feeding motivation. This contrasts with the locomotor activity decrease at proecdysis. Food consumption declined rapidly in D₁ and D₂ and ceased at the D₂-D₃ transition. Feeding resumed in B₁ or B₂, intensifying to maximum in late B₂. Feeding remained relatively constant within stages, whereas locomotor activity varied greatly, though both correlated with metabolic needs. Grouped and solitary lobsters displayed similar patterns of foraging and walking, equivalent to those of locomotor activity and feeding of solitary individuals. Frequency of agonistic interactions (not aggression per se) remained relatively constant through the cycle, peaking in metecdysis, though the highest relative proportion occurred near ecdysis. Lobsters then were submissive and avoided physical contact with conspecifics. Clearly, locomotor activity, feeding, and social behavior of P. argus are not simply determined. Indeed, behavior is distinctly phase coordinated with varying metabolic requirements dependent on the proximity to ecdysis and ecological pressures.     

Mitochondrial DNA variation and population structure in the spiny lobster Panulirus argus

Adult spiny lobsters (Panulirus argus) were collected from nine locations throughout the tropical and subtropical northwest Atlantic Ocean and examined for mitochondrial DNA (mtDNA) variation. 187 different mtDNA haplotypes were observed among the 259 lobsters sampled. Haplotype diversity was calulated to be 0.986 and mean nucleotide sequence-diversity was estimated to be 1.44%; both of these values are among the highest reported values for a marine species. Analysis of molecular variance (AMOVA) and phenetic clustering both failed to reveal any evidence of genetic structure within and among populations of P. argus. The present data are consistent with high levels of gene flow among populations of P. argus resulting from an extended planktonic larval stage and strong prevailing ocean currents.     

Cryptic species within the commercially most important lobster in the tropical Atlantic, the spiny lobster Panulirus argus

Panulirus argus (Latreille in Ann Mus Hist Nat Paris 3:388–395, 1804) is the lobster of greatest economic importance throughout its distribution. In this study, mitochondrial (Cytochrome Oxidase I and 16S ribosomal genes) and nuclear (Adenine Nucleotide Transporter gene) sequences were used to evaluate the taxonomic status of P. argus sampled from five sites in the Caribbean Sea and nine sites in the Southwest Atlantic. Phylogenetic analyses indicate that lobsters from the two regions form two monophyletic groups with a molecular divergence similar to that observed between distinct congeneric lobster species and much larger than that found between conspecific lobster populations. Therefore, the Caribbean and the Southwest Atlantic lobster populations originally attributed to P. argus belong to different species, with an estimated time of isolation of around 16 Million years. An important consequence of these findings is that the fisheries of spiny lobsters from the Caribbean and the Southwest Atlantic species must be managed separately.     

Control and coordination of reproduction and molting in the spiny lobster Panulirus argus

Behavioral and physiological correlates of vernal reproduction and molting were investigated experimentally in laboratory-held spiny lobsters (Panulirus argus Latreille) from Florida to determine their control by photoperiod and temperature. Behavioral measures included courtship, copulation and aggression; physiological measures included the timing and frequency of ecdysis, spermatophore emplacement, oviposition, egg hatching, and setal (pleopod) and gonadal development. Behavior resembled that observed in nature, as evidenced in the expression of complete reproductive cycles. Long daylengths and warmer temperatures enhanced courtship, spawning frequencies, and female gonadal development, although gonadal recrudescence occurred in large females irrespective of photoperiod. A significant interaction effect between photoperiod and temperature indicated a need to examine joint, non-independent factor effects upon reproductive parameters. Photoperiod and temperature did not significantly influence aggression and male gonadal development. Photoperiod did not affect molting rates significantly. However, warm temperatures enhanced molting and growth such that sub-adult and young adult lobsters (both sexes) had highest molting rates, followed by large adult males, which in turn had higher rates than reproductively active females. Female setal development correlated positively with female size, and changed abruptly at ecdysis. Although setal lengths were highly variable, setae of 9 mm or more signified sexual maturity. Reproduction and molting were size-dependent: the largest adults mated or spawned, the smallest molted, and intermediate-sized ones either mated, or molted before mating. Spiny-lobster reproductive and molting patterns were influenced by photoperiod and temperature in a complex manner depending upon sex, season, size and developmental state.     

Territory quality and territorial behavior in two sympatric species of hummingbirds

Summary Changes in territorial behavior of blackchinned hummingbirds (Archilochus alexandri) in response to experimental changes in territory quality were investigated using artificial feeders and simultaneous, pair-wise observations of owners. Some of the responses of A. alexandri were similar to those documented by a previous study of the Anna's hummingbird (Calypte anna): A. alexandri defending rich territories spent more time on their territories, encountered a greater percentage of intruders, and chased more intruders than did A. alexandri defending poor territories. In contrast to C. anna, A. alexandri supplemented chases with energetically inexpensive threat vocalizations more extensively when territory quality was increased. This difference may be related to A. alexandri's more tenuous control of rich territories. When both species were observed on very poor territories, A. alexandri chased a greater percentage of intruders, consumed a greater proportion of available food, and obtained a greater net energy gain from their territories. When observed simultaneously on territories with ad lib food, both species defended highly exclusive territories but A. alexandri suffered higher intrusion pressure and spent more time and energy in defense. These interspecific differences in territorial behavior may facilitate sympatric coexistence of the two species through aggressive partitioning of flower patches according to productivity: the greater payoff received by C. anna on rich territories and A. alexandri on poor territories should favor a corresponding monopolization of rich areas by C. anna and poor areas by A. alexandri.     

Temporal patterns and transport processes in recruitment of spiny lobster (Panulirus argus) postlarvae to south Florida

We used time-series analysis to identify weekly and annual patterns in the supply of spiny lobster, Panulirus argus (Latreille, 1804), postlarvae to the Florida Keys, USA, over an 8 yr period. We also investigated the relationship between postlarval influx and wind forcing as a transport mechanism using the complex vector-scalar correlation analysis. Postlarval supply had a lunar phase periodicity at 4.5 wk intervals, with postlarval abundance peaking between the new moon and first-quarter lunar phases. A distinct annual cycle of postlarval supply with two peak periods was also apparent. Cross-correlation analysis between relative postlarval abundance and a 12 mo cycle showed that the annual peak occurs in spring, centered around March. With the 12 mo periodicity removed, a smaller peak at 5 mo intervals was also well defined. Wind-forcing for 7 d prior to the time of postlarval collection was marginally correlated with postlarval abundance through the entire time-series; the association was strongest during the late fall to early spring months. The analysis indicated that postlarval supply was correlated with winds from the northeast (ca. 45°), which are associated with winter atmospheric fronts. In contrast to results reported for other spiny lobster populations, these patterns suggest that recruitment of lobster postlarvae to south Florida is predictable only at a gross level and is presumably affected by the temporally inconsistent structure of regional oceanic gyres and variability in the timing of lobster spawning in the Caribbean. Received: 24 January 1997 / Accepted: 4 March 1997     

Mitochondrial DNA sequence variation in spiny lobsters: population expansion,panmixia, and divergence

To investigate population differentiation in a comparative and historical context, segments of the mitochondrial cytochrome c oxidase subunit I gene and the control region were sequenced in Panulirus argus from nine sites along approximately 1,500 km of the Northern Caribbean Sea (n = 326) and analyzed with respect to available panulirid data. A mismatch analysis and Fu’s F _S test uncovered a signature of historical population expansion around the time of the Last Glacial Maximum. Significant population structure was not detected in the area. The data supported a hypothesis of panmixia resulting from ongoing larval transport by ocean currents and historical population expansion. Despite high intraspecific divergence levels at COI within Panulirus argus and several other Panulirus species, genetic species identification through DNA barcoding was feasible using either a modified distance threshold or a character-based approach.     

Asymmetric mate choice,hybridization, and hybrid fitness in two sympatric grasshopper species

Hybridization between animal species has long been regarded as unusual, but is meanwhile accepted as a widespread phenomenon. Typically, sexual interactions among species are studied in secondary contact zones of closely related species (hybrid zones) or between invasive and native species, whereas hybridization between sympatric congeners has received little attention. Here, we present a study on the hybridization potential of two grasshopper species, Chorthippus parallelus and Chorthippus montanus, which occur sympatric in large parts of Eurasia. We performed a mate choice experiment with specimens from an area of local parapatry in northwestern Germany. Most copulations were conspecific, but males of both species and females of C. parallelus were indiscriminate in their mate choice, while females of C. montanus clearly preferred conspecific males. Although these results suggest asymmetric introgression, a no-choice hybridization experiment revealed that hybridization is possible in both directions. The hatching success of the hybrids was intermediate between the parental species. Female hybrids showed no clear mate preferences, indicating that back crossing in both directions is possible in principle, but the fertility of the hybrids and the fitness of the F2 generation remain unknown. Our study suggests that hybridization between sympatric species might occur more often than assumed. It might affect the ecology and local distribution of animals in a similar way as competition does.     

Inter-specific variation in anti-predator behavior in sympatric species of kangaroo rat

Kangaroo rats, Dipodomys, occupy desert habitats with little cover and thus are under high predation risk from diverse predators. The behavior used to assess predation risk or to escape capture is unknown. We therefore compared anti-predator behavior of two sympatric species of kangaroo rat of different sizes, D. merriami and D. spectabilis. We first examined whether kangaroo rats use olfaction as a first line of defense against snake predation and tested the rats for their responses to scent extracted from two species of snake that live sympatrically with the kangaroo rats, the Mojave rattlesnake (Crotalus scutulatus) and the gopher snake (Pitophis melanoleucus). We also tested for species differences in anti-predator behavior through 15-min interactions between the kangaroo rats and free-moving gopher snakes. We found that D. spectabilis actively approached the scent of both rattlesnakes and gopher snakes more than controls of vegetable oil and evaporated solvent (Fig. 1). In contrast, D. merriami did not differentiate snake odors from controls in the experimental arena, but they sniffed the sand where a free-moving snake had passed more than D. spectabilis. Both species successfully avoided predation in encounters with live snakes. Although total numbers of approaches and withdrawals were similar (Fig. 2), D. spectabilis spent significantly more time within striking distance of the snake than D. merriami. D. spectabilis approached the head of the snake in 93% of its approaches and often engaged in nose to snout contact with the snake. If the snake struck, D. spectabilis jumped directly backward to avoid a strike and footdrummed at a safe distance. In contrast, D. merriami oriented to the snake more than D. spectabilis, but approached the head in only 41% of the approaches and rarely engaged in nose-to-snout contact. The snakes struck, hissed and decreased predatory approaches with D. spectabilis but not with D. merriami (Fig. 3). These results show that kangaroo rats can behaviorally influence the risk of being preyed on by snakes. The two species differ, however, in how they react to snakes. The larger D. spectabilis confronts snakes while the smaller D. merriami monitors snakes from a safe distance and avoids them.     

Population structure and reproductive biology of two sympatric hydrothermal vent polychaetes,Paralvinella pandorae and P. palmiformis

The alvinellid polychaetes Paralvinella pandorae Desbruyères and Laubier and P. palmiformis Desbruyères and Laubier occur at deep-sea hydrothermal vents along the Juan de Fuca and Explorer Ridges in the northeast Pacific Ocean. The population structure and reproductive biology of both species were studied in samples taken from three vent sites during six cruises in 1983 and 1984. Size-frequency analyses of two P. pandorae populations produced unimodal histograms, suggesting continuous or semi-continuous juvenile recruitment; in a third population two possible size classes were evident. Histograms of P. palmiformis displayed size-class peaks, which most likely reflected periodic recruitment of juveniles. Both species are gonochoric and gametes develop free in the coelom. Due to the simultaneous presence of a full range of gametogenic stages in P. pandorae populations, including spermatozoa in males, and to the continuous or semi-continuous recruitment pattern suggested by the size-frequency histograms, continuous reproduction is proposed for this species. In P. palmiformis a discrete, possibly synchronized, breeding cycle is thought to occur. Although maximum fecundity of P. pandorae is very low, continual reproduction over a long period of time could enhance its reproductive potential. The estimate of maximum fecundity for P. palmiformis is comparable to estimates for other polychaetes that undergo non-planktotrophic larval development. Maximum observed oocyte size was 215 and 260 m in P. pandorae and P. palmiformis, respectively. It is proposed that P. pandorae broods its young, while P. palmiformis probably undergoes demersal lecithotrophic larval development. The continual production of brooded young by P. pandorae could maintain a vent population, but severely limit dispersal to other vents. Demersal lecithotrophic larvae of P. palmiformis could repopulate vents, and potentially be carried by bottom currents to other vent sites.     

The breeding biology of two sympatric species of tropical intertidal hermit crabs,Clibanarius chapini and C. senegalensis

A one-year study of breeding in the two intertidal hermit crabs Clibanarius chapini Schmitt and C. senegalensis Chevreux and Bouvier showed that both species maintain a high reproductive activity throughout the year. Brief low reproductive activities, found in both species, occurred in different months: C. chapini in November, C. senegalensis in May. While these drops cannot be attributed to any recognisable environmental factor, it is suggested that such pattern may result from competition between the two species. Sex-ratio studies indicated slightly more females than males in both species. The maximal size attained by males of both species is considerably greater than that of the females; in C. senegalensis this is very marked. It is suggested that it may be selectively advantageous for a female to attain a smaller maximal size since her brood must also be accomodated within the shell. As expected for continuously breeding species, recruitment of young into the population is also continuous.     

Scent mediation of intraspecific,interspecific, and intergeneric agonistic behavior among sympatric species of voles (Microtinae)

Summary The hypothesis that the posterolateral scent glands of male microtine rodents (Muridae) direct the attacks of other males was tested.Montane voles (Microtus montanus) and sagebrush voles (Lagurus curtatus) were established as residents in terraria, and conspecific and heterospecific males, from which posterolateral scent glands had been unilaterally removed, were introduced. More attacks by residents were aimed at the glandular sides than at the glandless sides. Male M. montanus also attacked the unilateral hip gland of longtail voles (M. longicaudus), the growth of which had been induced by exogenous hormone inasmuch as this species does not normally possess these glands. Resident male M. longicaudus did not similarly attack the induced glands of conspecific males.The findings are related to demographic patterns, mterspecific relationships, and the evolutionary development of posterolateral scent glands among microtine rodents.     

Comparative study of sympatric populations of two hyperiid amphipods,Primno johnsoni and P. evansi,from the eastern North Atlantic Ocean

Hyperiid amphipods are common components of oceanic plankton communities, and yet information is lacking on the ecology and biology of the majority of species. This study compares sympatric populations of two phrosinids, Primno johnsoni Bowman and P. evansi Sheader, using material collected on R.R.S. Discovery Cruises 121 and 140 in the eastern North Atlantic Ocean. The two species were essentially very similar in terms of their vertical distribution and diurnal migration, and in the timing and sequence of reproductive events (onset of maturity, ovary/oocyte development, marsupial development). Mature female and male size ranges were comparable for the two species, males maturing at a small body size, with little subsequent growth, and females producing a succession of 5 (P. evansi) or 6 (P. johnsoni) broods maximum. The species differed significantly in egg size and in total egg output. These dissimilarities were accentuated by differences in the patterns of female mortality in the two species, such that actual egg output per female was 1.8 times greater (2.4 times in terms of total egg volume) in P. johnsoni than in P. evansi. These differences were reflected in the relative size of populations in the field. Although both species are capable of consuming a wide range of planktonic prey, it is assumed that gelatinous species are important, especially as hosts for the parasitoid juvenile stages, and it is suggested that host-specificity might act to separate the niches.     

Reproductive isolation and reproductive output in two sympatric mussel species (Mytilus edulis, M. trossulus) and their hybrids from Newfoundland

The mussels Mytilus edulis L. and M. trossulus Gould are found sympatrically in most areas of Newfoundland, with a low frequency of hybrids. To assess the potential for reproductive isolation, we sampled mussels from three sites in an eastern Newfoundland Bay from May–October 1996 to determine if there were differences in the reproductive cycles of the two species and their natural hybrids. In mussels with sheil lengths of 38–42 mm, males and females with mature gametes were dominant in June for M. edulis and hybrids, while M. trossulus showed a lower frequency of individuals with mature gametes. M. trossulus and hybrids spawned over a prolonged period (from late spring to early autumn) compared with most M. edulis individuals that spawned over a period of 2–3 weeks in July. This asynchrony in spawning activity between the two species may partially explain the low frequency of hybrids found in previous studies of these mussel populations. Female and male hybrids between M. edulis and M. trossulus showed normal gonad development, ripening and spawning, providing an opportunity for the introgression of genes between the two species. M. trossulus had a higher reproductive output than M. edulis of similar shell length, while hybrids showed intermediate values of reproductive output. M. trossulus females produced smaller eggs than either M. edulis or hybrids. Differences in reproductive traits may partially explain the maintenance of the mussel hybrid zone in Newfoundland. Published online: 13 August 2002     

Reproduction of sympatric populations of Patiriella gunnii,P. calcar and P. exigua in New South Wales,asterinid seastars with direct development

Three asterinid seastars, Patiriella gunnii (Gray), P. calcar (Lamarck) and P. exigua (Lamarck) are sympatric in southeast Australia and form part of a series of Patiriella species endemic to Australian shores. Reproduction of co-occurring populations of P. gunnii, P. calcar and P. exigua was investigated in New South Wales from December 1988 to February 1991. Their reproductive cycles were documented by the gonad index (GI) method and by histological examination of the gonads. The annual cycle of the pyloric caecae was also documented and the relationship between the two indices was examined. Oogenesis and spermatogenesis are described in histological detail. The three species produce large yolky eggs and have direct development. Vitellogenesis and weight-gain by the ovaries results from accumulation of periodic acid Schiff (PAS +) material by the oocytes. P. gunnii and P. calcar are gonochoric and have well-defined reproductive cycles, spawning in spring and summer. There was a sharp decline in the GI of P. gunnii in December due to potentially synchronous spawning. Histological examination revealed that initiation of gamete release occurred in August. Gamete release by P. calcar also started in August, with episodic spawning through December. P. gunnii and P. calcar have coincident 3 to 4 mo breeding seasons. In general, P. exigua is protandrous with a broad size range over which sex change occurs. Some P. exigua, however are simultaneous hermaphrodites at the outset of gonad formation and become increasingly female with growth. This species has continuous gametogenesis and oviposits its eggs on the undersides of intertidal boulders, with enhanced oviposition during winter and spring. Newly metamorphosed P. exigua occupy intertidal microhabitats and were located in the field from August to October. It is suggested that increasing sea temperature during spring may serve to cue gamete release by P. gunnii and P. calcar and that enhanced oviposition of P. exigua in winter may be in response to conditions optimal for development of the egg masses at this time. The GI of male and female P. gunnii and P. calcar did not differ, while male P. exigua had a significantly lower GI than the females. Small males are characteristic of this latter species, and it is suggested that the decreased male investment in P. exigua is associated with its non-planktonic development. The gonad and pyloric caeca (PCI) indices of P. gunnii exhibited a reciprocal relationship, indicating that the transfer of nutrients from the caeca to the gonads supports gametogenesis. These indices were partly reciprocal in P. calcar. It is suggested that gonadal growth in P. calcar may be less dependent on caecal reserves than that in P. gunnii. The PCI of P. exigua maintained a similar level throughout the year and was higher than the GI. Although the Patiriella species have coincident breeding periods, temporal differences in the intensity of spawning appears to reproductively isolate them in the field.     

Habitat selection of two congeneric bivalves,Cardium edule and C. glaucum in sympatric and allopatric populations

Habitat selection of two bivalve species, Cardium edule (L.) and C. glaucum (Bruguière) is described for sympatric and allopatric populations of both sibling species. It is demonstrated that C. edule grows faster than C. glaucum and is absent from localities with periodic low food-availability. The ability to burrow of C. glaucum is low compared with that of C. edule; the former species does not occur in very loose, well-sorted sand near the coast. Earlier studies which suggest that tidal range determine the species distribution could not be confirmed.     

Reproduction,recruitment and fragmentation in nine sympatric species of the coral genus Acropora

Multispecies assemblages of the coral genus Acropora occur commonly throughout the Indo-Pacific Ocean. Nine species from such an assemblage comprising 41 species of Acropora, at Big Broadhurst Reef on the Great Barrier Reef, were studied during 1981–1983. Similarities and differences in reproductive modes and timing, oocyte dimensions and fecundity, recruitment by larvae and by fragments, and mortality were recorded. All species had an annual gametogenic cycle, were simultaneous hermaphrodites, and had the same arrangement of gonads in polyps. In six species, most colonies released gametes on the same night of the year, in early summer, during a mass spawning event involving many coral genera. A seventh species had colonies spawning at this as well as other times of the year. Another species spawned in late summer, and gametes were not observed to mature in the last species. Eggs were very large (601 to 728 m geometric mean diameter) and fecundity of polyps low, compared with other corals; no reduction in oocyte numbers occurred during oogenesis. Reef-flat species had slightly bigger and fewer eggs than reef-slope species. All species recruited by larvae, but four also multiplied by fragmentation, either year-round or during occasional rough weather. Yearround fragmenters had few larval recruits; non-fragmenters had many, and a rough-weather fragmenter had an intermediate number of larval recruits. It was concluded that larval recruitment largely determined species composition, and that reduced larval recruitment was responsible for sparse distribution of fragmenting species. Subsequent mortality in some species and increase by fragmentation in others probably determined relative abundances.