Reproductive Peak Research Articles

Evaluating the importance of demographic connectivity in a marine metapopulation

Recently researchers have gone to great lengths to measure marine metapopulation connectivity via tagging, genetic, and trace-elemental fingerprinting studies. These empirical estimates of larval dispersal are key to assessing the significance of metapopulation connectivity within a demographic context, but the life-history data required to do this are rarely available. To evaluate the demographic consequences of connectivity we constructed seasonal, size-structured metapopulation matrix models for two species of mytilid mussel in San Diego County, California, USA. The self-recruitment and larval exchange terms were produced from a time series of realized connectivities derived from trace-elemental fingerprinting of larval shells during spring and fall from 2003 to 2008. Both species exhibited a strong seasonal pattern of southward movement of recruits in spring and northward movement in fall. Growth and mortality terms were estimated using mark-recapture data from representative sites for each species and subpopulation, and literature estimates of juvenile mortality. Fecundity terms were estimated using county-wide settlement data from 2006-2008; these data reveal peak reproduction and recruitment in fall for Mytilus californianus, and spring for M. galloprovincialis. Elasticity and life-stage simulation analyses were employed to identify the season- and subpopulation-specific vital rates and connectivity terms to which the metapopulation growth rate (lambda) was most sensitive. For both species, metapopulation growth was most sensitive to proportional changes in adult fecundity, survival and growth of juvenile stages, and population connectivity, in order of importance, but relatively insensitive to adult growth or survival. The metapopulation concept was deemed appropriate for both Mytilus species as exchange between the subpopulations was necessary for subpopulation persistence. However, highest metapopulation growth occurred in years when a greater proportion of recruits was retained within the predominant source subpopulation. Despite differences in habitat and planktonic duration, both species exhibited similar overall metapopulation dynamics with respect to key life stages and processes. However, different peak reproductive periods in an environment of seasonal current reversals led to different regional (subpopulation) contributions to metapopulation maintenance; this result emphasizes the importance of connectivity analysis for spatial management of coastal resources.

Seasonal and annual variation in Chilean hake Merluccius gayi spawning locations and egg size off central Chile

Variability in Chilean hake reproductive tactics off central Chile was assessed by analyzing ichthyoplankton samples from nine oceanographic cruises (1996–2005) and through experimental trials with early life stages (eggs, yolk-sac larvae) during the main (austral spring) and secondary (late summer–early autumn) spawning seasons. Abundant eggs in the plankton (1300–2000 eggs per 10 m 2) and historical adult reproductive data showed the highest reproductive activity in austral spring, with large egg aggregations near shelf break (50–100 m depth). Large, recently spawned eggs (1.15–1.20 mm diameter) were advected nearshore by coastward subsurface flows in the spring upwelling season. Experimental trials indicated that recently hatched larvae (3.4–3.5 mm) consumed their yolk-sac (0.17–0.41 mm 3) in 3–4 days at 10–12 °C; plankton sampling indicated that larval hake remained at mid-depth (50–100 m) without showing daily vertical migrations until completing their caudal fin formation (∼15 mm). During the secondary reproductive peak, hake spawned nearshore, when smaller eggs (0.95–1.13 mm) and recently hatched larvae (2.2–2.6 mm notochord length) occurred in surface waters (0–10 m depth). Their relatively large yolk-sac volumes (0.57 ± 0.11 mm 3) provided endogenous nourishment for at least 5 days at 10 °C, according to experiments. In the field, preflexion larvae occurred mainly in the mixed layer (0–25 m) and started ontogenetic daily vertical migrations at 7 mm. A strong decline occurred after 2002 in the adult Chilean hake biomass (estimated by hydroacoustic surveys) and body size, coinciding with variations in spawning locations (more coastward in early spring 2004 and 2005) and decline in egg size. Thus, recent variations in Chilean hake reproductive tactics may reflect an indirect effect of declines in the parental population size.

석묵 (Campylaephora hypnaeoides)의 생장과 성숙에 대한 야외 및 배양 연구

The phenology of Campylaephora hypnaeoides J. Agardh and optimal conditions for carpospore release, growth and reproduction were examined in the field and in the laboratory from January to December 2007. In the field population of C. hypnaeoides, approximately 50% of the plants were vegetative during the study period. Additionally, the percentages of carposporophytes and tetrasporophytes were maximal in April (37%) and June (57%), respectively. Maximum growth in plant length, dry weight, and hook number coincided with the tetrasporophyte reproductive peak in the field. In culture, carpospore release, sporeling growth and reproduction were affected by environmental factors such as daylength, temperature, and salinity. The liberation of carpospores was maximum under continuous light and at a combination of <TEX>$15^{\circ}C$</TEX> and <TEX>$10\;{\mu}mol$</TEX> photons <TEX>$m^{-2}\;s^{-1}$</TEX>. Maximum growth of tetrasporophyte sporelings occurred at a combination of <TEX>$20\;{\mu}mol$</TEX> photons <TEX>$m^{-2}\;s^{-1}$</TEX> of constant light and <TEX>$25^{\circ}C$</TEX>. However, the growth of gametophyte sporelings was maximal under <TEX>$40\;{\mu}mol$</TEX> photons <TEX>$m^{-2}\;s^{-1}$</TEX> of constant light and in a combination of <TEX>$20^{\circ}C$</TEX> and 35 psu. The tetrasporophyte sporelings were grew faster than gametophytes, indicating that gametophyte- and tetrasporophyte-sporelings have different physiological responses to irradiance and temperature. Tetrasporangial branches and cystocarps of C. hypnaeoides were produced from carpospores and tetraspores within 1 month, and they were stimulated at high temperature and irradiance levels. In conclusion, C. hypnaeoides should be seeded using carpospores during early winter (November-December) because cystocarps are easily identified by fishermen, and tetrasporophytes grow faster than gametophytes.

The environmental setting and microfauna of the oligohaline Timsah pond, Israel: The last remnant of the Kabara swamps

Abstract Enot Timsah is a spring-fed wetland ecosystem at the foot of the Carmel Mountain, a relict of the much larger Holocene Kabara swamps, at the northern outlet of the Yarqon-Tanninim mountain aquifer. This groundwater-surface water interaction zone supports a unique living foraminiferal and ostracod fauna. Sampling of water and sediment was carried out approximately monthly in 2002/3 as part of a study of the species richness and history of this distinctive ecosystem. Enot Timsah is nearly isothermal (23.98 ± 0.4 °C) and oligohaline with total dissolved solids (TDS) of 3,213 ± 118.5 mg/l. The water column is transparent and highly oligotrophic, with very low phosphate concentration. Living ostracods and Rose Bengal stained benthic foraminifera occur in low numbers. A monospecific population of the ostracod Cyprideis torosa lives at the surface, with a reproductive peak in April, 2002. Foraminifera occur throughout the topmost 0–4 cm. Extreme oligotrophy of this ecosystem means that there is a low flux of phytoplankton, limiting abundance of surface-dwelling ostracods and foraminifera. Microbial decomposition of vascular plant debris was the food source for infaunal foraminifera. The low salinity means that living conditions are marginal explaining low numerical abundance of foraminifera. However, foraminiferal diversity is exceptionally high at Enot Timsah compared with other oligohaline environments, with 15 living benthic taxa and three additional species found in the dead assemblage. The living assemblage is composed of cosmopolitan agglutinants known to live in brackish environments, together with some calcareous hyaline and miliolid taxa. The exceptional foraminiferal diversity is attributed to four factors: the very stable conditions of salinity and temperature; the high Ca2+ and HCO3− concentrations derived from the karstic aquifer (promoting mineralization of calcareous tests), the maturity of the Kabara ecosystem dating from the early Holocene; and the repetitive reintroduction of cosmopolitan brackish foraminifera by avian transport. Increased numbers of living foraminifera with abnormal morphologies testify to stress conditions. Dead foraminifera are more abundant than living ones, with agglutinated foraminifera dominating the living assemblage, and calcareous forms dominating the dead assemblage. This taphonomic reversal is attributed to microbial decomposition of organic cement of the agglutinants, while the calcareous forms are resistant to dissolution because of the high Ca2+ and HCO3− of the aquifer-derived spring waters. The Holocene fossil record of the predecessors of the Kabara swamps therefore represents an estimated 10–40% of the information found in the living foraminiferal assemblage at Timsah.

Zygote-derived seedling production of Sargassum thunbergii: focus on two frequently experienced constraints in tank culture of seaweed

Mass collection of germlings and growth of fouling algae are two main constraints for the seedling production of Sargassum thunbergii. In this study, 65% and 40% of reproductive output (allocation of biomass to sexual reproductive tissue) for farmed and natural populations respectively, were recorded during peak reproduction. In terms of germlings per kilogram wet weight of plants, the farmed population gave a higher yield than the natural population (3.2 × 105 and 1.2 × 105 germlings kg-1, respectively). These results indicate that farmed populations could be used as parental plants for germling collection in seedling production. During the experiment, fouling was controlled by jet washing and high-density seeding. A germling detachment of less than 10% was observed when, after 48 h of attachment, collectors were jet-washed with an intensity of 1 kg cm-2. High-density seeding had adverse effects on length mean, size equality, and occurrence of branches of germlings. However, 30–50 individuals cm-2 are thought to be usable in the seedling production of S. thunbergii because of less density effects. Seedlings of > 0.5 cm length could be achieved after 1 month of tank culture.

Reproductive phenology of Brazilian savannas and riparian forests: environmental and phylogenetic issues

The reproductive phenology of plants is expected to be influenced by climatic factors and by the phylogenetic history of the species. In savannas, the peaks of flowering and fruiting are associated with climate seasonality. However, there is still a controversy about the reproductive phenology of plants in riparian forests, a vegetation type that does not experience a severe water shortage. We tested whether the reproductive peaks in riparian forests are different from those of the savannas. We also tested if the number of species in flower is correlated with rainfall and day length. We sought evidence of phylogenetic signals in the reproductive periods of the species. Most of species in savannas and riparian forests flowered and fruited in the wet season. The number of flowering species was positively correlated with monthly rainfall and day length. However, we did not find phylogenetic signals in the reproductive periods. The phenological pattern of riparian forests was similar to that of savannas. At the community level, the reproductive periods of plants may not be under phylogenetic constraints, as observed in forests under nonseasonal climate. Sun-related variables seem to be the main cues for the reproductive phenology of plants in savannas and riparian forests.

Reproductive biology of the broad-snout [Chondrostoma holmwoodii (Boulenger, 1896)] in Tahtalı Dam Lake, İzmir, Turkey

The study aimed to determine the reproductive characteristics of the broad-snout Chondrostoma holmwoodii population (spawning season, number of eggs and first age of sexual maturity) in order to assess the population status in the Tahtalı Dam Lake reservoir. A total of 1208 specimens were examined of which 72.1% were females and 27.9% males (female:male ratio = 1 : 0.40); the percentage of males, however, declined in the higher age classes (IV and V). The monthly determined gonadosomatic index indicated that the peak reproduction period of the species is in April and early May. The study covered age classes I–V, with specimens at age II reaching maturity. The total number of eggs per female varied from 8000 to 41 700, the mean number of eggs increasing proportionally with age of the spawner. Egg diameters also increased during the 5-month ripening period from December to April.

Reproductive strategies of two sympatric swimming crabs Callinectes danae and Callinectes ornatus (Crustacea: Portunidae) in an estuarine system, south-eastern Brazil

The present study analysed the reproductive biology of Callinectes danae and Callinectes ornatus, which are captured as by-catch from pink-shrimp trawling in Guanabara Bay. The size at gonadal maturity was 79.9 mm and 67.4 mm respectively, for C. danae and C. ornatus. The pattern of reproduction was continuous for both species; however, the gonadosomatic index analyses showed seasonal and alternating reproductive peaks in the bay. While C. danae showed reproductive peaks in the autumn and in the winter, C. ornatus showed an apparent reproductive peak in the summer and probably another in the spring. The sex-ratio of C. danae was significantly skewed in favour of females (3.0:1). However, in C. ornatus, males predominated (1.2:1). This reproductive pattern indicated that possibly the females of C. danae return to the estuary after spawning where trawling takes place, while ovigerous females of C. ornatus migrate to adjacent coastal areas around the bay.

Oithona brevicornis Giesbrecht (Copepoda: Cyclopoida), invader into the Black Sea and in the Sea of Azov

The pattern of distribution and biology of a cyclopoid copepod Oithona brevicornis new to the northeastern shelf of the Black Sea was studied. Penetration of this species will probably change the trophic structure of mesozooplankton in the neritic zone. From late August to November 2010, O. brevicornis was a predominant species in mesozooplankton, reaching 80–85% of its total amount. In September, its maximum density in Novorossiysk Bay reached 30 000 ind./m3; in Gelendzhik Bay and Anapa Bay and in Lake Zmeinoe (Big Utrish), it was 22 000–27 600 ind./m3. In August 2010 O. brevicornis was recorded in the Sea of Azov. In the period of peak of reproduction of the pelagic predator ctenophore Mnemiopsis leidyi A. Agassiz in the Temryuk Gulf, its abundance varied from 4 to 600 ind./m3.

Contrasting reproductive strategies in three deep-sea octocorals from eastern Canada: Primnoa resedaeformis, Keratoisis ornata, and Anthomastus grandiflorus

Various aspects of reproduction were studied in three deep-sea octocorals belonging to the order Alcyonacea that co-occur at bathyal depths on the continental edge and the slope of eastern Canada. The main goals were to expand knowledge of deep-water heterotrophic corals and ascertain whether reproductive strategies could explain the known patterns of occurrence. Anthomastus grandiflorus is a gonochoric species with a female-biased sex ratio that exhibits internal fertilization and brooding of planula larvae. Conversely, Primnoa resedaeformis and Keratoisis ornata rely on broadcast spawning and external fertilization; their sexuality remains undetermined as spermatocysts were not found. In P. resedaeformis, the presence of mixed size classes of oocytes in samples from all months, depths, and locations studied suggests continuous oogenesis or overlapping development of oocyte cohorts, indicative of a gametogenic cycle spanning more than a year. No evidence of periodicity was found in this species, although it could have been masked by the striking bathymetric variation in potential relative fecundity (oocytes polyp−1). The two other octocorals displayed a clear annual breeding pattern. Spawning in K. ornata and larval release in A. grandiflorus occurred in late summer and fall, respectively, possibly in response to environmental factors, as supported by shifts in the reproductive peak of A. grandiflorus across latitudes. The three species are presumed to share a nonfeeding larval mode, and data on their reproductive potential do not present any striking disparities. Published data on bycatches and video surveys in Atlantic Canada indicate that the gonochoric brooder A. grandiflorus is more widely distributed than the two free spawners, P. resedaeformis and K. ornata, which is contrary to common dispersal potential paradigms.

Seasonal dynamics in population characteristics of European bitterling Rhodeus amarus in a small lowland river

The seasonal dynamics of biological traits in a population of European bitterling Rhodeus amarus from a small river in central Europe (River Kyjovka, Czech Republic) were investigated from April 2007 to March 2008. The reproductive season lasted from early April to mid-June, with a peak in late April when > 50% of females possessed ripe eggs in their ovaries. The sex ratio was female-biased, with a higher bias following the peak in reproduction, suggesting higher mortality of males than females over the reproductive period. The population was effectively annual, with a major decrease in adult fish abundance at the end of the reproductive period. Highest relative lipid content and condition factor were observed in February, both decreasing with an increase in investment into gonads. Seasonal dynamics in somatic condition, relative lipid content and gonad mass, and their comparison with other R. amarus populations, suggest that the study population allocated a disproportionally high level of resources to reproduction.

Biology and population dynamics of the black-flanked rock-wallaby (Petrogale lateralis lateralis) in the central wheatbelt of Western Australia

Through a mark–recapture study, we explored aspects of the biology and population dynamics in the largest known population of the black-flanked rock-wallaby (Petrogale lateralis lateralis) at Mt Caroline Nature Reserve, in the Western Australian wheatbelt in 2007–10. The body condition index of males and females varied significantly over time but fluctuated similarly for both sexes. Males and females followed a pattern of best condition in early summer, declining through autumn and reaching their poorest condition in early spring. Body condition was closely related to rainfall in the period ~3–6 months before trapping sessions. Births occurred throughout the year with two reproductive peaks, in autumn and late winter/spring. Reproductive rates averaged over 90% annually, except in 2007 when they averaged 76%. Significantly fewer females bred during 2007, and those females were in poorer body condition. Females with a higher body condition index were more likely to reproduce (P = 0.003) but body condition did not influence the sex of offspring. The sex ratio of offspring did not differ significantly from parity and did not support either the Trivers–Willard or local resource competition hypotheses. This information should help to predict population trends and develop appropriate conservation strategies for this threatened species.

Reproductive Cycle Observation of the Okinawa Rail (Gallirallus okinawae) in the Wild

The captive breeding program of the Okinawa rail started in 2008. For successful captive breeding, information related to reproduction, such as age at sexual maturity, testicular cycles and ovulatory cycles, is essential to predict when reproduction is possible and when certain reproductive behaviors are most likely to occur. We made gross and histological observations of the reproductive organs of Okinawa rails to gain understanding of sexual maturity, the testicular cycle and the ovulatory cycle. We found that the weight of the testis was smallest in December and largest in March. Changes in the diameter of the seminiferous tubule showed the same pattern. Mature sperm were observed from March to June. The heaviest ovary was observed in April. A single peak of reproduction, from March to April, was observed in males and females. Our observations suggested that the Okinawa rail is a seasonal breeder. Establishing suitable breeding pairs will be critical to ensure success of the Okinawa rail captive breeding program. Our results suggested that pairing must be started before March. If supportive breeding is used, semen should be collected from March to June and artificial insemination conducted in April.

Reproductive characteristics of the bathyal viviparous fish &lt;i&gt;Cataetyx alleni&lt;/i&gt; (Osteichthyes: Bythitidae) from the southeastern Sardinian Sea (central-western Mediterranean) MARIA

The reproductive biology of the bathyal viviparous fish Cataetyx alleni was described based on 34 specimens (17 females and 17 males) caught during experimental trawl surveys carried out between 800 and 1700 m depth in the southeastern Sardinian Sea (central-western Mediterranean). Males and females were present at similar size intervals. For the first time, the internal fertilization was demonstrated by the finding of free spermatozoa scattered in the ovarian cavity. Based on macroscopic and histological gonad analysis, mature females were found in summer, autumn and winter, suggesting a long reproductive period. Inseminated females were observed only in November and January, in correspondence with the higher maturity of the males. These results suggest a probable reproductive peak with copulation in autumn-winter. Moreover, histological examination demonstrated that the ovaries of this member of the family Bythitidae had a ‘group-synchronous’ pattern. No spermatophores in males and embryos in females were observed in the histological sections analysed.

Rates of post-larval bedload dispersal in a non-tidal soft-sediment system

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 416:145-163 (2010) - DOI: https://doi.org/10.3354/meps08796 Rates of post-larval bedload dispersal in a non-tidal soft-sediment system Sebastian Valanko1,2,3,*, Alf Norkko1,2,4, Joanna Norkko1,2,3 1Marine Research Centre, Finnish Environment Institute (SYKE), 00251 Helsinki, Finland 2Tvärminne Zoological Station, 10900 Hanko, Finland 3Environmental and Marine Biology, Åbo Akademi University, 20520 Åbo, Finland 4Department of Marine Ecology - Kristineberg, University of Gothenburg, 45034 Fiskebäckskil, Sweden *Email: sebastian.valanko@ymparisto.fi ABSTRACT: Quantifying rates of dispersal and understanding patterns of colonization are key for predicting disturbance–recovery dynamics. For soft-sediment benthic communities recruitment is not restricted to one single event, but can be highly variable on several spatial and temporal scales. To investigate the temporal persistence of post-larval bedload transport in a non-tidal system, field experiments were conducted at 4 sites (5 m depth) across a wind-wave exposure gradient over 2 summers. Results indicate that bedload dispersal is temporally variable and dependent on an interaction between species-specific characteristics (including seasonal peaks in reproduction), site-specific hydrographic conditions, grain size characteristics and transport of sediments and drift algae. Dispersal of more passive taxa (Ostracoda, juvenile gastropods, Macoma balthica) was found to be associated with higher rates of sediment and algal transport, while more active species (Hydrobia ulvae and Potamopyrgus antipodarum) dispersed relatively more at sheltered sites. At higher rates of sediment transport, there was an increase in the proportion of larger M. balthica individuals dispersing, in contrast to Hydrobiidae, which had an increased proportion of smaller individuals. Our study suggests that frequent post-larval dispersal plays a central role in the population dynamics of many benthic invertebrates, in non-tidal systems. While the distribution of species is heavily influenced by peaked larval recruitment over large spatial scales, the net result of continuous small-scale dispersal events is clearly important and may contribute to the resilience of benthic communities. KEY WORDS: Invertebrate · Benthos · Baltic Sea · Mobile · Recruitment · Connectivity Full text in pdf format PreviousNextCite this article as: Valanko S, Norkko A, Norkko J (2010) Rates of post-larval bedload dispersal in a non-tidal soft-sediment system. Mar Ecol Prog Ser 416:145-163. https://doi.org/10.3354/meps08796Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 416. Online publication date: October 14, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Spawning and reproductive potential of the Northern stock of Argentine hake ( Merluccius hubbsi)

The reproductive activity of the Argentine hake Merluccius hubbsi Northern stock takes place mainly during autumn and winter in the Argentine Uruguayan Common Fishing Zone (AUCFZ) (34°30′–39°30′ S and 52–59° W). At the present scarce information about spawning pattern and reproductive potential of M. hubbsi of this area is available. Therefore, the purpose of this work is to analyze variation of the spawning area, estimate batch fecundity, spawning frequency, oocyte dry weight and size at maturity of Northern stock of Argentine hake. The results showed that the main reproductive activity of this hake stock during April 2003 occurred between 37° and 38°30′ S while in May 2009 spawning groups moved north to the 37° S. In both cases reproduction took place near the 50 m isobath, in a temperature range between 9 and 15 °C, in coincidence with a bottom thermal front. Size at maturity for hake males (25.7 cm TL in April 2003 and 26.8 cm TL in May 2009) was significantly less than that estimated for females (29.3 cm TL in April 2003 and 32.6 cm TL in May 2009), and also showed significant differences for individuals of the same sex in different years. Spawning frequency, estimated in one spawning every 13 days during May 2009, was about haft to that reported for the Southern hake stock, which distributed between 41° and 55° S. Batch and relative fecundity values estimated for the Northern stock in April 2003 showed no significant differences with data obtained in May 2009, and were similar with those obtained for the Southern stock during its reproductive peak. The oocyte dry weight for spawning females of the Northern stock was lower than that estimated for the Southern stock, which might be associated with the size composition of each reproductive group.

Reproductive performance of the crayfish Procambarus ( Austrocambarus) acanthophorus Villalobos 1948 under controlled conditions

Aspects of the reproductive biology of the crayfish Procambarus acanthophorus were documented under controlled conditions to determine this species’ culture potential. A completely random experimental design with three replicates was used to evaluate three different male/female sex ratios (1 M:1F, 1 M:3F and 1 M:5F) with 12 organisms (TL > 30 mm) per replicate. The experimental culture system was a closed recirculating system with constant water flow (2 L .min − 1 ), and once daily ad libitum feeding with a 35% protein commercial diet. Recorded reproductive parameters were peak reproduction season, fertility index, egg viability and female length at first sexual maturity. Peak reproduction activity occurred during November–December, the lowest activity in February–March, and no differences were observed between treatments. Fertility was estimated as a function of egg count per female ( n = 25) and hatch rate. The highest ( p < 0.05) number of ovigerous females was produced at the 1 M:3F ratio, and the lowest at the 1 M:5F. Average egg count per female was 240.9 (± 93.1) and average egg viability was 29.1% (± 31.7). The relationship between total length and egg count was positive and significant ( r 2 = 0.654), although the relationship between length and egg viability was not ( r 2 = 0.1132). Average female length at first sexual maturity was 34 mm. The study results indicate P. acanthophorus can be effectively reproduced in captivity under controlled conditions and is therefore a candidate for use in commercial aquaculture activities.

Habitat associations, reproduction and diet of the Guinean tilapia Tilapia guineensis of the Gambia River floodplains

The ecology of the Guinean tilapia Tilapia guineensis a dominant species of the lower Gambia River floodplains and an important food source in parts of West Africa was studied to better understand the threat posed from construction of a barrage across the river. The catch per unit effort (CPUE) of T. guineensis was positively associated with conductivity and dissolved oxygen and negatively associated with water depth and the % vegetation cover. Diet studies indicated that the T. guineensis is primarily an iliophage. The peak of reproduction was at the beginning of the rainy season. CPUE peaked in May, just before the first rains, and subsequently declined, probably reflecting movement into newly flooded habitat. Median size at maturity was 11.6 cm total length, L(T), for females and 12.5 cm L(T) for males. L(T)-frequency analysis indicated several juvenile cohorts as well as very young fish on the floodplains each month, suggesting continuation of reproduction throughout the rainy season. The impending construction of a hydroelectric dam on the Gambia River is likely to affect T. guineensis negatively through anticipated changes in the hydrology of the river.

Temporal changes in the reproductive population structures and males’ secondary sexual character of the hermit crab Diogenes nitidimanus

AbstractWe investigated the reproductive ecology of D. nitidimanus in the Waka‐River estuary with special reference to temporal change in the relative size of chelae length for males, i.e., secondary sexual character. Ovigerous females were observed from April to October, peaking in June–July with over 90% of females being ovigerous. Adult female carapace size ranged from 3.5 to 8.5 mm, but with the majority of females falling between 5–6 mm. Male carapace length was more evenly distributed between 3.5 and 10 mm. Juvenile settlement occurred mostly in July, during which time the frequency of both large females (over 6.5 mm in carapace length) and large males (over 8.5 mm in carapace length) clearly decreased. The carapace length of precopulatory‐guarded females varied from 4.8 to 8.0 mm, while guarding males were almost over 7 mm and always larger than their paired females. The relative growth of the major chelae differed significantly between small and large males during the early months of the year, including the reproductive peak months (April–June). During these early months, large males had relatively larger chelae for their body size than did small crabs. This difference, however, was not evident later in the year (July–September). Large males may grow their chelae relatively long in the early months in order to take advantage of the mating opportunities during April–June. This is the first report in animals, to our knowledge, that relative size of the secondary sexual character for males temporarily change during a single reproductive season.

Biology of the Armored ScaleRhizaspidiotus donacis(Hemiptera: Diaspididae), a Candidate Agent for Biological Control of Giant Reed

AbstractThe development, survival, and reproductive output of the armored scale Rhizaspidiotus donacis Leonardi (Hemiptera: Diaspididae) were determined as part of an evaluation of this scale for biological control of giant reed, Arundo donax L. Scale crawlers produced by females collected in southern France and Spain lived for less than two d in the absence of a host. On A. donax shoots held under a diurnally variable temperature regime (15–26°C), crawlers settled on leaf collars and axillary stem bases and completed the first instar within 14 d. Winged adult males emerged within six wk and lived 1.7 d in vials. Immobile adult females were observed 75 d after crawler release. Development time to adult was reduced 15% in males and 28% in females when scales were reared at a constant temperature of 26°C. Survival from crawler to adult was 20–25%. The generation time for laboratoryreared females was 170d and their average life span was 203 d. Females from field collections produced an average of 85 live crawlers, 2.7-fold more than did colony-reared females. Across 31 field collections, female size was correlated to the percentage of scales that were reproductive. However, among eight collections from two Spanish sites, size varied but was not correlated to reproductive success. Peak reproduction from field collections occurred between November and March, and the scale completed two generations per year. Biological information about R. donacis will aid production, release, and field evaluation of this scale for biological control of invasive A. donax in North America.