Resource partitioning by four species of elasmobranchs (Batoidea: Urolophidae) in coastal waters of temperate Australia

Four species of stingarees (Urolophus lobatus, U. paucimaculatus, Trygonoptera personata and T. mucosa) were abundant in samples collected from over sandy substrates in four regions along ∼200 km of the lower west coast of Australia in each season between summer 1990/1991 and winter 1992. The main aim of this study was to determine whether these four species were segregated by habitat, size, sex and/or diet, thereby reducing the potential for intra- and interspecific competition. The densities of U. lobatus and T. personata were almost invariably greater in deep, offshore waters (20 to 35 m) than in shallow, inshore waters (5 to 15 m), while those of U. paucimaculatus were greatest in the southernmost region, irrespective of depth, and those of T. mucosa were highest at the single inshore site at which the water was deep. None of these species was segregated by either size or sex. The volumetric dietary compositions of the two Urolophus species, which consisted predominantly of various crustaceans, and those of the two species of Trygonoptera, which consisted mainly of different polychaetes, were significantly different from each other. The two Urolophus species initially fed largely on amphipods, mysids and carid decapods but, with increasing size, U. lobatus started to ingest teleosts and U. paucimaculatus commenced feeding on errant polychaetes and penaeid decapods. The contribution of errant polychaetes to the diets of T. personata rose progressively from 0% in the smallest fish to 90% in the largest fish, thereby accounting for a concomitant progressive decline in dietary breadth and for intraspecific dietary overlap typically to occur only between successive size classes. In contrast, the volumetric contribution of sedentary polychaetes to the diets of T. mucosa remained high (65 to 80%) throughout life, which accounts for the relatively low and constant dietary breadth of most size classes and a significant overlap in the diets of all but one pair of size classes. The diets of each of the four stingaree species occasionally differed between sites and sometimes underwent seasonal changes, presumably reflecting spatial and temporal differences in the types of prey in the environment. Since the ratios of benthic to epibenthic prey in the diets of the two Trygonoptera species were greater than in those of the two Urolophus species, the first two species apparently forage deeper into the substrate. The combination of partial segregation of the four stingaree species among habitats and the differences in the dietary compositions and feeding strategies of these species, would presumably facilitate the co-existence of these batoid elasmobranchs when they are abundant in the same general region. Received: 29 October 1997 / Accepted: 25 March 1998     

Relationships between the movements,growth, age structures,and reproductive biology of the teleosts Sillago burrus and S. vittata in temperate marine waters

Sillago burrus and S. vittata both use sheltered, nearshore shallow waters ( 1.5 m) as nursery areas. However, the juveniles of the former species remain there for only a few months, before migrating into deeper waters (5 to 15 m) as they increase in size, whereas some juvenile S. vittata do not undergo a similar migration until considerably later. S. burrus rarely exceeded 2 yr of age and was never found beyond 4 yr of age. Although only a small number of S. vittata exceeded 2 yr of age, a few individuals of this species were caught between 4 and 7 yr old. The maximum and asymptotic lengths of S. burrus (251 and 180 mm, respectively) were far lower than those of S. vittata (325 and 320 mm, respectively), whereas the growth coefficients (K) were much higher for the former species, i.e. 2.4 vs 0.4. Virtually all S. burrus, and also those S. vittata that moved into deeper waters early in life, spawned at the end of their first year of life. Since relatively few S. burrus reached 2 yr of age, the attainment of almost full size by the end of their first year of life enables a relatively large number of eggs to be produced by fish at the end of their first year-for many, their only spawning period. Those individuals of S. vittata that remained in their shallow nursery areas until the end of their first year of life, did not reach maturity until the end of their second year of life. The proportions of mature gonads and the numbers of yolk-vesicle and yolk-granule oocytes and post-ovulatory follicles in ovaries were far higher in both S. burrus and S. vittata during December to February than in any other month, demonstrating that these two species spawn largely in these summer months. During this period, the ovaries of individual S. burrus and S. vittata often contained post-ovulatory follicles, as well as yolkvesicle and yolk-granule oocytes that ranged widely in size, strongly suggesting that both species are multiple spawners. During the spawning period of S. burrus, the ovaries possessed large numbers of hydrated oocytes and no post-ovulatory follicles or the reverse situation, and the oocytes tended to form several relatively discrete size groups. This indicates that S. burrus produces eggs in batches and that the spawning of the members of this species is synchronised. The presence of large numbers of yolk-granule oocytes with migrating nuclei in the ovaries of many S. vittata at certain times suggests that this species is also a batch- and synchronised spawner. Comparisons between the results of the present study and past work emphasise that the relationships between the timing of offshore movements and the sizes and ages at first maturity vary considerably amongst whiting species.     

New data on reproductive biology and growth of Octopus vulgaris

The problems of reproduction of Octopus vulgaris and the seasonal distribution in the sea of planktonic larvae, benthonic juveniles and adults are discussed. The influence of environmental factors on growth is shown by experimental studies in the laboratory, and the difficulties of interpreting field data are emphazised.Dedicated to Professor Dr. Adolf Portmann on his 75th birthday, 27 May, 1972Laboratoire associé au C.N.R.S.     

Sex pheromone composition and reproductive isolation in two Busseola species (Lepidoptera: Noctuidae) in Kenya

Closely related species provide an interesting and useful model to understand mate communication diversification. Pre-mating isolation is the result of selection processes and is achieved by utilization of different sex pheromones, but also by different ecological and life traits such as geographic distribution, host-plant specialization and allochrony of sexual behavior. Here, we report sex pheromone identifications and pre-mating isolation of two closely related species of stemborers: Busseola segeta and the yet undescribed Busseola nov. sp., developing on different host-plants and in different geographical locations in Kenya. GC–MS analyses showed that the two species produced the same pheromone components, but in slight different ratios. The respective synthetic pheromone mixtures tested in the field were attractive for males of each species. The low inter-specific variation in the pheromone mixture would allow possible interbreeding in case of accidental introduction of both species in the same environment. Under laboratory conditions, allochrony of the mating period is total and might prevent interbreeding if confirmed in natural conditions. This point would ensure the reproductive isolation between the two species in case of modifications of ecological factors. This study and the chemical structures of the identified pheromone components clearly demonstrate that these Busseola species are closely related although they differ in morphology.     

Relationship between fruit growth and peduncle cross-sectional area in durian (Durio zibethinus Murray)

The relationship between fruit growth and peduncle cross-sectional area in the tropical tree Durio zibethinus Murray growing in an experimental field of Universiti Putra Malaysia (UPM), was examined. Fruit dry mass was allometrically related to the product of lateral and longitudinal fruit diameters by a power function, and the mass growth rate of the fruits was linearly related to the peduncle cross-sectional area. This linear relationship indicates that the specific fruit growth rate, defined as the fruit mass growth rate per unit cross-sectional area of peduncle, is constant. On the basis of previous findings of proportionality between the fruit growth rate and the rate of translocation of photosynthates into the fruit through the peduncle, it was concluded that fruit growth rate, translocation rate and peduncle cross-sectional area are proportional to each other.     

Population dynamics and reproductive biology of the commensal isopod Colidotea rostrata (Crustacea: Isopoda: Idoteidae)

Colidotea rostrata (Benedict, 1898) is the only known commensal idoteid isopod, living on and mimicking the color of two northeastern Pacific sea urchins of the genus Strongylocentrotus. The population dynamics and reproductive biology of C. rostrata on its host urchins were studied at a low rocky intertidal area in southern California (33°40N; 118°30W) from December 1984 to December 1986. Isopod populations remained relatively stable throughout the 2 yr study, with isopods inhabiting an average of 56.1% of the urchins at 6.1±0.6 (x±2 SE) isopods per urchin. Female isopods reach sexual maturity at a length of 6.8 mm. Fecundity in C. rostrata averaged 11.8±0.9 (x±2 SE) embryos per brood, and increased with female body size. Breeding occurs all year long in C. rostrata, with a main reproductive period between the warmer spring and summer months. Newly released mancas and juvenile isopods were present during all months of the study. C. rostrata differs from the free-living Idoteidae in its smaller maximum size, reduced fecundity, 1:1 sex ratio, and low juvenile mortality. These features may represent adaptations to a commensal life style that reflect a reduced mortality pressure on these isopods.     

Latitudinal variation in the reproductive biology of the burrowing ghost shrimp Callianassa filholi (Decapoda: Thalassinidea)

Population structure and reproductive ecology of the burrowing ghost shrimp Callianassa filholi Milne-Edwards, 1878 were studied in populations along a latitudinal gradient throughout New Zealand during the breeding season. Size-frequency distributions revealed unimodal populations, with predominantly sexually mature shrimp. All populations showed an unbiased sex-ratio, and there appeared to be no significant difference in size (carapace length, CL) between sexes. At the same time, CL and size at maturity differed significantly between populations; however, a general increase in sizes from north to south was not consistent throughout the latitudinal range studied. The timing of the breeding cycle differed significantly between populations, and breeding started earlier in southern populations. Number of embryos (fecundity) increased linearly with female CL at each location, but rates differed significantly between populations. Embryo size was not related to number of embryos, and the former increased significantly with latitude. With the exception of embryo size, observed differences in body size/size at maturity and reproductive timing between C. filholi populations are thought to be determined by food availability rather than temperature. Thus, further study is suggested on these aspects of thalassinid reproductive biology. Received: 17 June 1999 / Accepted: 8 January 2000     

Sex ratio varies with egg investment in the red-necked phalarope (Phalaropus lobatus)

Fisher’s sex ratio theory predicts that on average parents should allocate resources equally to the production of males and females. However, when the cost/benefit ratio for producing males versus females differs, the theory predicts that parents may bias production, typically through underproduction of the sex with greater variation in fitness. We tested theoretical predictions in the red-necked phalarope, a polyandrous shorebird with sex-role reversal. Since females are larger and therefore potentially more expensive to produce and may have greater variation in reproductive success, we predicted from Fisher’s hypothesis a male bias in population embryonic sex ratio, and from sex allocation theory, female biases in the clutches of females allocating more resources to reproduction. We measured eggs and chicks and sexed 535 offspring from 163 clutches laid over 6 years at two sites in Alaska. The embryonic sex ratio of 51.1 M:48.9 F did not vary from parity. Clutch sex ratio (% male) was positively correlated with clutch mean egg size, opposite to our prediction. Within clutches, however, egg size did not differ by sex. Male phalarope fitness may be more variable than previously thought, and/or differential investment in eggs may affect the within-sex fitness of males more than females. Eggs producing males were less dense than those producing females, possibly indicating they contained more yolk relative to albumen. Albumen contributes to chick structural size, while yolk supports survivorship after hatch. Sex-specific chick growth strategies may affect egg size and allocation patterns by female phalaropes and other birds.     

Relationship between growth rate and age at recruitment ofAnguilla japonica elvers in a Taiwan estuary as inferred from otolith growth increments

The growth history and recruitment dynamics of eel (Anguilla japonica) elvers were studied. Observations were based on growth increments in sagittal otoliths of elvers collected from Shuang-Chi River estuary off northeastern Taiwan, from November 1985 to February 1986. Total lengths of elvers upon arrival at the estuary were similar in most case; mean total lengths were from 55.99 to 59.06 mm. Daily ages of elvers at arrival ranged from 112.8±9.4 (±SD) to 156.5±13.5 d, indicating that migration of eel larvae from their oceanic spawning ground to the estuary requires 4 to 5 mo. Elver hatching dates, back-calculated from estimated daily ages, indicated that the spawning season lasted 5 mo (from late June to early October). Furthermore, the earlier eels spawned, the earlier elvers reached the estuary. The transition in growth history during the larval stage was obvious, as indicated from the change in increment width in elver otoliths. The inverse correlation between daily age and mean daily growth rates of fish length and otolith indicated that the age of elvers upon arrival at the estuary was susceptible to larval growth rate. In other words, the time taken on migration from oceanic spawning ground to the estuary was shorter for fast-growing larvae than for slowgrowing ones.     

Demography and reproductive biology ofMelinna palmata (Ampharetidae: Polychaeta) in Inner Galway Bay on the west coast of Ireland

A high-density population of the polychaeteMelinna palmata Grube was the focus of a two-year study at a shallow-water location in Inner Galway Bay on the west coast of Ireland. Mean densities were highest in the second year of the study following successful recruitment. Size-frequency analysis of population structure (April 1983 to March 1985) revealed the presence of four cohorts, with the 1983 settlement becoming the dominant modal class. Size comparison of this cohort with the 1982 settlement showed that growth rates were lower and mortality higher in the 1983 settlement, which may be related to density dependent intra-specific competition.M. palmata at this location live for 2 to 2.5 yr with a small number surviving to 3 yr of age.M. palmata in Galway Bay is dioecious and has an even sex ratio. Reproductively mature worms were approximately 2 yr old when they first spawned. Spawning took place between May and July, when mature oocytes had a modal size of ca. 290µm. Proliferation of previtellogenic oocytes (ca. 10µm) from the gonads occurred following spawning. Growth over the winter was slow and was followed by a period of rapid growth between March and May, coincident with rising water temperatures. The presence of mature unspawned oocytes, which were resorbed after commencement of new proliferation, was taken as evidence of the species propensity for polytely. However, post-spawning mortality appeared to be high, so that only a small number of individuals survived to spawn the following year. The highest abundance of mature males was encountered between May and August, but lower levels of mature stages were present throughout the year.     

Population structure and reproductive biology of Ceratonereis limnetica (Polychaeta: Nereididae) at Lower Portland,Hawkesbury River,Australia

Ceratonereis limnetica Hutchings and Glasby was collected from Lower Portland, Hawkesbury River, New South Wales, Australia, from March 1982 to September 1983. C. limnetica is one of a relatively few polychaete species in which the adults normally tolerate reverine conditions. Reproduction in this species has been modified accordingly, differing from the common pelagic spawning of many nereidids. Adults of both sexes remain essentially unmodified and spawn on the bottom. Embryos and larvae are brooded in specially constructed tubes in the sediment by the female. Both sexes have a life span of about 1 yr, dying soon after spawning. The morphological and reproductive behavioural similarities between C. limnetica and C. aequisetis are considered to indicate a close phylogenetic affinity.     

Latitudinal variation in the reproductive biology of the commensal crab Pinnaxodes chilensis (Decapoda: Pinnotheridae) along the Chilean coast

The pinnotherid crab Pinnaxodes chilensis is a common commensal of the edible sea urchin Loxechinus albus along the Chilean coast. Several aspects of the reproductive biology of P. chilensis were examined between April and June 1999, along temperature and salinity gradients, at three sampling sites along the Chilean coast (23°45'S-39°24'S). Results demonstrated significant differences in egg number, egg volume, dry egg weight, and reproductive output of ovigerous females, between the studied populations of northern and central-southern Chile. Egg volume, egg dry weight, and reproductive output of females decreased from high to low latitudes, while egg number increased from high to low latitudes, exhibiting a clear trade-off with egg volume. It has been shown that changes in environmental conditions (e.g. temperature, salinity) along a latitudinal gradient, can generate clines in reproductive characteristics in both free-living and parasitic species.     

Effect of diet on growth rate and reproductive fitness of Turbo sarmaticus (Mollusca: Vetigastropoda: Turbinidae)

Experiments were conducted to determine the effect of four algal diets (Corallina spp., Gelidium pristoides, Ulva rigida and an equal volume mixture of these seaweeds) on growth and reproduction of the South African gastropod Turbo sarmaticus Linnaeus, 1758. The best growth rate of juveniles (up to 13.8 mm shell length and 34.26 g wet body weight increase in 12 months), reproductive fitness of mature specimens (gonad index up to 33%) and energy reserves (up to 4.76 mg glycogen/100 mg foot tissue) were achieved when T. sarmaticus was fed U. rigida or a mixed diet. In addition, the gonad index of individuals fed these diets was almost twice that of similar-sized field specimens. Juveniles fed Corallina spp. only, grew very little (only 2.4 mm shell length and 4.23 g wet body weight increase in 12 months). The reproductive fitness of adults fed on such a diet was also poor (gonad index <4.5%) and energy reserves were low (<3.5 mg glycogen/100 mg foot tissue). Along the southeastern coast of South Africa, T. sarmaticus has a distinct reproductive cycle with gametogenesis occurring from March/April until August/September, whilst maturity (gonad index = 15%) was maintained until December, after which spawning occurred until March. Received: 6 July 1998 / Accepted: 8 March 1999     

Fecundity and reproductive effort in Ophryotrocha labronica (Polychaeta: Dorvilleidae)

Reproductive effort in terms of fecundity and energy allocation was studied in Ophryotrocha labronica La Greca and Bacci, 1962 a small, semicontinuous iteroparous species. In O. labronica fecundity is more or less constant throughout life, and the total fecundity of the 64 couples examined in this experiment only declined by 12% from the first to the last spawning. No linear relationship was found between fecundity and body size.␣The energy content of germinal and somatic tissues was determined by differential scanning calorimeter. The␣reproductive effort and a reproductive index based on the fifth spawning were evaluated to compare the␣patterns of energy allocation of a semicontinuous iteroparous species with semelparous and annual iteroparous species. The reproductive index ranged from 0.20 to 0.77, with an average of 0.480. The average reproductive effort was 0.840, ranging from 0.60 to 0.96. These figures highlight the enormous amount of energy that O. labronica allocates to reproductive tissues. Received: 23 July 1997 / Accepted: 20 October 1998     

Chemical composition of Eurasian lynx urine conveys information on reproductive state,individual identity,and urine age

In mammals, the chemical profiles of individuals are complex and variable mixtures, and animals perceive information based on variation in the overall quality of these mixtures. A variety of compounds potentially involved in chemical communication have been characterized in the urine of different felid species, but little is known about the information content of felid scent marks. In this study, we investigated whether chemical composition of Eurasian lynx Lynx lynx urine was related to sex, reproductive state, and individual identity. We further analysed if elemental sulphur in lynx urine could serve as a dietary cue or as an indicator for the freshness of a scent mark. We collected urine from captive and wild Eurasian lynx, and analysed volatile constituents of urine by means of solid phase microextraction and gas chromatography-mass spectrometry. Our results show that lynx scent profiles contain sex-specific information on reproductive state, as well as individual identity cues. Urine marks are, therefore, well-suited to fulfil a role in reproductive behaviour and social organisation of wild lynx populations. Relative sulphur content was unrelated to time since last feeding, but decreased with age of the urine sample. The influence of diet and body condition on scent profiles should be further investigated by means of experimental studies, and may shed more light on the messages encoded in carnivore scent-marks.     

Otolith record of age, growth, and ontogeny in larval and pelagic juvenile Stephanolepishispidus (Pisces: Monacanthidae)

Juveniles of the planehead filefish Stephano-lepishispidus (Pisces: Monacanthidae) (Linnaeus, 1766) are a major component of the Sargassum spp. community, yet little is known of their ecology. In this study, the otolith record of age, growth, and ontogeny in S. hispidus was examined. Juveniles caught off Beaufort Inlet, North Carolina (USA) on 30 June 1996 were marked with alizarin complexone and reared in a flow-through, outdoor tank for up to 19 days. Examination of marked otoliths at several time intervals showed that increment formation was not significantly different than one increment per day, and thus, increment number was used to estimate age. Depth-distribution, morphology, and meristics of larvae and juveniles collected (1990–1992) between Cape Romain, South Carolina, and Cape Hatteras, North Carolina, were examined to identify the timing of the larval to juvenile transition. All indicators suggested the transition occurred between 17 and 20 days. Mean otolith increment widths exhibited a marked change at about 20 days, coinciding with the timing of the larval to juvenile transition and a change in the depth distribution from bottom to surface waters. Increment width of individual juveniles, however, did not exhibit the same pattern; only 40% conformed to the pattern identified for all fish. Thus, the record of the larval to juvenile transition is clear at the population level, but unresolved at the individual level. Received: 1 November 1999 / Accepted: 18 December 2000