Temporal Patterns Of Reproduction Research Articles

Body size and condition, not allochrony, affect temporal reproductive patterns in a prolonged breeding anuran

Body size and condition, not allochrony, affect temporal reproductive patterns in a prolonged breeding anuran

Seasonal heterochrony of reproductive development and gene expression in a polymorphic salamander.

Life cycle evolution includes ecological transitions and shifts in the timing of somatic and reproductive development (heterochrony). However, heterochronic changes can be tissue-specific, ultimately leading to the differential diversification of traits. Salamanders exhibit alternative life cycle polymorphisms involving either an aquatic to terrestrial metamorphosis (biphasic) or retention of aquatic larval traits into adulthood (paedomorphic). In this study, we used gene expression and histology to evaluate how life cycle evolution impacts temporal reproductive patterns in males of a polymorphic salamander. We found that heterochrony shifts the distribution of androgen signaling in the integument, which is correlated with significant differences in seasonal reproductive gland development and pheromone gene expression. In the testes, androgen receptor (ar) expression does not significantly vary between morphs or across seasons. We found significant differences in the onset of spermatogenesis, but by peak breeding season the testes were the same with respect to both histology and gene expression. This study provides an example of how seasonal heterochronic shifts in tissue-specific ar gene expression can disparately impact seasonal development and expression patterns across tissues, providing a potential mechanism for differential diversification of reproductive traits.

Expansion and contraction of the Engraulis ringens spawning area in northern Chile

Many studies have considered the temporal patterns of reproduction of Engraulis ringens, but little attention has been given to the spatial patterns of reproduction (spawning areas), which have shown great variability in both location (geographical position) and extent (the area covered by positive stations), without a satisfactory explanation. Along the Chilean coast, the daily egg production method (DEPM) has been used for several years to estimate spawning biomass in the northern Chile E. ringens population, with 24 surveys being carried out from 1992 to 2020. The most fluctuating parameters estimated in the DEPM have been the location and extent of the spawning area and the average female weight. In the last few years the eggs were distributed near the coast, whereas in the first few years they showed a more oceanic distribution. The average female weight has fallen from 30 g in the 1990s to 11 g in the last few years. In the present study, we analysed the relationship of the location and extent of spawning areas with female size and abundancy in E. ringens from northern Chile. According to the results, periods of high abundancy of eggs are positively correlated with larger females that spawn in more oceanic zones and to the south, expanding the spatial egg distribution and increasing the egg density. By contrast, in years with low abundance of eggs, the spawning was located north and towards the coast, with a smaller spawning area and smaller female size.

Climate drives anuran breeding phenology in a continental perspective as revealed by citizen‐collected data

AbstractAimAs anuran reproduction is generally linked to the availability of water, frogs and toads are particularly sensitive to climate. We tested the effect of climate on anuran reproductive phenology and daily activity by analysing temporal patterns of reproductive behaviour based on citizen‐collected observations.LocationBrazil.MethodsWe obtained vocalizations and photographs of frogs with inflated air sacs, as well as images of amplectant couples, nests, eggs or tadpoles in initial stages of development from iNaturalist. We analysed hourly patterns, seasonality and duration of the reproductive period using circular statistics in different climate types and tested phylogenetic signals. We analysed data for Bufonidae, Hylidae, Leptodactylidae and Phyllomedusidae in detail. We also reviewed relevant literature.ResultsAmong the 8478 (acoustic and photographic) records, 738 (8.7%) had evidence of reproduction with 284 acoustic records and 454 photographs, representing 184 taxa identified at the species level belonging to 16 families. Climate affected the period and duration of the reproductive season, as well as daily patterns of vocalization. These results were considered phylogenetically independent, as the reconstructions of ancestral character states did not suggest strong phylogenetic signals for temporal patterns of vocalization or reproduction. In Brazil, most frogs reproduce between October and January. Patterns were similar to the results of the literature review, however in the literature data, Bufonidae start reproduction 2 months earlier, and many Hylidae species reproduce until February. In general, frogs from warmer and drier climate regions had shorter and aggregated reproductive seasons, while in tropical monsoon climate they had a uniform temporal pattern.Main conclusionsAt the continental scale, reproductive phenology of anurans and their daily activity is affected by climatic conditions regardless of phylogeny. We found that community science can provide valuable information in Brazil that can be harnessed to monitor effects of climate change on amphibian reproduction.

Proximate drivers of population inter-annual variation in seed output for a masting conifer species

Assessing the drivers of population inter-annual variation in reproductive output (CVp) is key for conservation and management of forest resources, as these drivers determine variation in seed crops which are closely related to seedling recruitment (i.e. forest regeneration) and understanding the mechanisms by which they affect reproductive output sheds light into population-level resilience to changing abiotic conditions. Proximate drivers of CVp include weather conditions which act as cues for reproduction and resource-driven lagged negative autocorrelations between past and current reproduction. Increased temporal variability in weather cues and strong negative autocorrelations are both expected to increase CVp, but very few studies have robustly tested these predictions at the intra-specific level using long-term, multi-population datasets. Based on a published dataset, we used approximately 2,000 yearly observations spanning 130 years (1886–2015) and 61 populations to test for effects of temporal variability in weather cues and lagged autocorrelations on CVp in seed output for a masting conifer species (Picea abies). We found that lagged (lag –1) summer (June–July) mean temperature was the best predictor of population-level annual seed output. Contrary to expectations, however, we observed a significant negative (not positive) effect of the standard deviation of lag –1 summer mean temperature on CVp. In addition, we found a non-linear, hump-shaped relationship between lag –1 reproductive autocorrelation and CVp, suggesting a qualitative change in the effects of resource constraints on reproductive variability whereby expected positive effects change to negative when the strength of negative autocorrelations exceeds a certain level. These patterns point at unexpected mechanisms whereby temporal variability in weather cues dampens variability in reproductive output, whereas the non-linear association with the lagged autocorrelations suggest thresholds associated with resource availability leading to qualitative changes in temporal patterns of reproduction.

Impacts of a drought and hurricane on tropical bird and frog distributions

AbstractDuring the last few decades, much attention has focused on how global change is affecting the environment and species distributions. Land‐use change is still the major cause of species declines worldwide, but changes in species distributions have been documented even in pristine and protected areas. Here, we document the distribution dynamics of 26 species of frogs and birds within a Caribbean protected area between 2015 and 2019. Specifically, we document species occupancy and detectability in 59 sites along three elevational transects within the El Yunque National Forest in Puerto Rico. Species were sampled using acoustic recorders, species identification algorithms, and post‐classification validation. The study period included a severe drought (2015–2016) and a category 4 hurricane (2017). The distribution of most frog species did not change significantly during the study period. In contrast, the distributions of the bird species contracted between the 2015 and 2016 pre‐hurricane surveys. This contraction coincides with a severe drought that peaked after the 2015 survey. The response of bird species after H. Maria was heterogeneous. Our results suggest that for many species, particularly birds, the 2015–2016 drought in Puerto Rico had a greater negative effect than H. Maria. The difference in the response of the bird and frog communities is likely related to their abundance at the site level, their ability to disperse, and temporal patterns of reproduction. If a site is occupied by a frog species, it could easily include 100s of individuals, and even if condition worsens, over a relatively short period the species will continue to occupy the site. In contrast, a site may only be occupied by one or a few individuals of birds. Birds have also higher dispersal abilities than frogs. Furthermore, Puerto Rican frogs reproduce year‐round, whereas birds concentrate their reproduction during a few months in the wet season. Future climate scenarios predict a decrease in total precipitation and an increase in droughts for the region, which emphasizes the need to consider the diversity of changes that will be associated with future climate change.

Reproductive Parameters for Female Beluga Whales (<i>Delphinapterus leucas</i>) of Baffin Bay and Hudson Bay, Canada

Monitoring marine mammal populations and their habitats is crucial for assessing population status and defining realistic management and conservation goals. Environmental and anthropogenic changes in the Arctic have prompted the pursuit for improved understanding of female beluga whale (Delphinapterus leucas) spatial and temporal reproductive patterns. There are relatively few estimates for female reproductive parameters of beluga whale populations across the Arctic, and those few that are available are outdated. Here we summarize female reproductive data from samples collected through Inuit subsistence hunts of three eastern Canadian Arctic beluga populations: High Arctic/Baffin Bay (HA), Western Hudson Bay (HB), and Cumberland Sound (CS) from 1989 to 2014. We grouped the CS and HA populations into a Baffin Bay region (BB) population based on similar body growth patterns and genetic similarity. Asymptotic body length of BB beluga whales (370.9 cm) was greater than HB whales (354.4 cm) as established from Gompertz growth curves fitted for whales ranging in age from 1 – 89 y. We did not detect a significant difference in average number of pseudocervices (8.6) between regions. Differences in average age of sexual maturity (ASM) and length at sexual maturity (LSM) were identified, with evidence of BB females maturing earlier than females from HB (probability method BB = 9.9 y versus HB = 11.0 and logistic method ASM50% HB = 9.99 and BB unresolved). BB females were also longer than HB females at maturing age (logistic LSM50%: BB = 314.5 cm vs HB = 290.3). Total corpora counts were strongly correlated with age, although the number of corpora (≥ 10 mm) suggests reproductive senescence between 40 and 50 y. Improved understanding of female reproductive patterns and knowledge of changes in the spatial and temporal timing of reproductive processes are fundamental for effective conservation and sustainable management of beluga whale populations.

Chemical signatures of femoral pore secretions in two syntopic but reproductively isolated species of Gal\xe1pagos land iguanas (Conolophus marthae and C. subcristatus)

The only known population of Conolophus marthae (Reptilia, Iguanidae) and a population of C. subcristatus are syntopic on Wolf Volcano (Isabela Island, Galápagos). No gene flow occurs suggesting that effective reproductive isolating mechanisms exist between these two species. Chemical signature of femoral pore secretions is important for intra- and inter-specific chemical communication in squamates. As a first step towards testing the hypothesis that chemical signals could mediate reproductive isolation between C. marthae and C. subcristatus, we compared the chemical profiles of femoral gland exudate from adults caught on Wolf Volcano. We compared data from three different years and focused on two years in particular when femoral gland exudate was collected from adults during the reproductive season. Samples were processed using Gas Chromatography coupled with Mass Spectrometry (GC–MS). We identified over 100 different chemical compounds. Non-Metric Multidimensional Scaling (nMDS) was used to graphically represent the similarity among individuals based on their chemical profiles. Results from non-parametric statistical tests indicate that the separation between the two species is significant, suggesting that the chemical profile signatures of the two species may help prevent hybridization between C. marthae and C. subcristatus. Further investigation is needed to better resolve environmental influence and temporal reproductive patterns in determining the variation of biochemical profiles in both species.

Within- and between-year variations of reproductive strategy and cost in a population of Siberian chipmunks.

Reproduction costs depend on the general life-history strategies employed by organisms for resource acquisition, the decision rules on resource allocation, and the resource availability. Although the predictability of resource availability is expected to influence the breeding strategy, the relationship between predictability and strategy has rarely been investigated at the population level. One reason is that, while the resource availability is commonly variable in space and time, their predictability is generally assumed constant. Here, we addressed the temporal variation of the breeding strategy and its associated survival cost in a hibernating population of Tamias sibiricus, in which food resources vary in their availability between years and in their predictability within years. Based on 11years of mark-recapture data, we used multi-event modelling to investigate seasonal variations in reproduction costs of female chipmunks that breed twice a year (spring and summer). In summer, during which a large variety and quantity of resources is available (income breeding strategy), the proportion of breeding females was consistent across years and reproduction yielded no mortality cost. In contrast, in spring, the proportion of breeding females was positively correlated with the amount of resources available for hibernation (partial capital breeding strategy). Spring reproduction yielded no immediate cost, but induced a delayed mortality cost over the next winter if future unknown conditions were unfavorable. Our findings highlight complex temporal reproductive patterns in a short-lived species: not only does the modality of resource acquisition vary among seasons, but also the decision rule to breed and its associated cost.

Spatial and temporal distribution of ichthyoplankton during an unusual period of low flow in a tributary of the São Francisco River, Brazil

AbstractFlow‐dependent fish specialists require specific conditions for reproduction, so the success and reproductive intensity of these animals are determined by the flood regime. Thus, this study investigated the spatial and temporal reproductive patterns of fish, especially migratory Prochilodus species (flow‐dependent specialists) in an unusual period of low flow in the Pará River sub‐basin, one of the main tributaries of the upper São Francisco River. For this, ichthyoplankton collections were carried out between November 2013 and February 2014. Data were analysed considering the spatial and temporal variations in density of eggs and larvae for the upper, middle, and lower portions of the Pará River sub‐basin, and correlating this to some environmental variables. The results showed that the small headwater stretch of the Pará River is one relevant spawning area for migratory fish species. However, this area is isolated by the Cajuru reservoir, which makes it uncertain the recruitment of these embryos, due to interruption of natural drift between spawning/nursery areas caused for reservoirs. Larvae of newly hatched migratory species found in tributaries of the lower Pará River sub‐basin also indicate these species use these tributaries as spawning grounds and migratory routes. The period in which the research was conducted represented the most atypical low flow, one in the last 75 years, resulting in the low variability in the environmental parameters. Although few parameters increased briefly in this low flow period influenced by greater rainfall in December, this precipitation was possibly responsible for the final gonadal maturation and spawning of migratory species.

Old-Growth Fishes Become Scarce under Fishing

Researchers have long recognized the importance of ecological differences at the species level in structuring natural communities yet until recently have often overlooked the influence of intraspecific trait variation, which can profoundly alter community dynamics [1]. Human extraction of living resources can reduce intraspecific trait variation by, for example, causing truncation of age and size structure of populations, where numbers of older individuals decline far more with exploitation than younger individuals. Age truncation can negatively affect population and community stability, increasing variability in population and community biomass [2-6], reducing productivity [7-10] and life-history diversity in traits such as the spatial and temporal pattern of reproduction and migration [4, 11-16]. Here, we quantified the extent of age truncation in 63 fished populations across five ocean regions, as measured by how much the proportions of fish in the oldest age groups declined over time. The proportion of individuals in the oldest age classes decreased significantly in 79% to 97% of populations (compared to historical or unfished values, respectively), and the magnitude of decline was greater than 90% in 32% to 41% of populations. The pervasiveness and intensity of age truncation indicates that fishing is likely reducing the stability of many marine communities. Our findings suggest that more emphasis should be given to management measures that reduce the impact of fishing on age truncation, including no-take areas, slot limits that prohibit fishing on all except a narrow range of fish sizes, and rotational harvesting.

The effects of resprouting natural forest on reproductive traits of blue tits (Cyanistes caeruleus) in a stone pine afforestation

The reproductive performance achieved by blue tits (Cyanistes caeruleus) in a low-quality habitat with a regular grid of nest boxes during a 6-year period (2007–2012) was tested. The variables used as sources of variation for analysis were the habitat quality (resprouted holm oak abundance) in the territories, the spatial distribution of territories (peripheral or interior nest boxes), the entrance-hole size of available nest boxes, the social context around the nesting territories (breeding neighbour density: conspecific or Great tits Parus major) and temporal pattern of reproduction (laying date). For whole breeding population, the proportion of successful nests and the breeding success were dependent on the location of territories and entrance-hole of nest boxes. The prediction concerning the relationship between habitat quality and reproductive performance is supported only for clutch size. This trait, but not the hatching and breeding success, clearly depended on resprouted holm oak abundance in the territories, increasing with the abundance of trees. Blue tits exhibited a clustered territoriality and the conspecific and Great tit P. major densities around blue tit territories were mutually influenced in a negative way. The breeding success variation in successful nests is positively associated to the conspecific density: individuals with more conspecific neighbours achieved best breeding success. For all nests pooled (successful and unsuccessful), reproductive performance was not dependent on the great tit density. Reproductive failure was higher in the large-holed nest boxes than in the small-holed ones. The clutch size also showed a significant gradient as a function of the egg-laying date: females laying eggs earlier in the season had larger clutch sizes than those who did later. From these results, we draw some implications for the management strategies of hole-nesting passerines using nest boxes in large areas of stone pines plantations.

Reproductive strategies of two invasive sun corals (Tubastraeaspp.) in the southwestern Atlantic

The azooxanthellate sun coralsTubastraea coccineaandT. tagusensisare invasive species which were introduced into Brazilian shallow-water tropical rocky reefs by oil and gas platforms. Both species are simultaneous hermaphrodites and brooders. Histological analysis shows a continuous reproduction with the presence of different stages of development of oocytes, spermatic cysts and larvae occurring together in the same polyps (overlapping). Gametogenesis, embryogenesis, planulation and settlement were observed. Although most of the colonies showed only oocytes, none had only testes. Spermatic cysts were observed in 8.3% ofT. coccineacolonies and in 5.5% of colonies ofT. tagusensis. The maximum diameter of oocyte ofT. tagusensis(1252.5 µm) was greater thanT. coccinea(901.8 µm) and mature spermaries 700 µm in diameter formed the typical arrangement of ‘bouquets’. Although all colonies showed oocytes throughout the year, two reproductive peaks of 3–4 months duration were observed. The larvae ofT. coccineaandT. tagusensishad a competency period of 18 d in aquaria and settled near the parental colony. The investigation of gametogenesis, temporal patterns of reproduction, fecundity and sexual maturation helps to explain the rapid expansion in to new habitats and high population growth in these invasive sun corals.

The advertisement and release calls of Melanophryniscus pachyrhynus (Miranda-Ribeiro, 1920) from the central region of Rio Grande do Sul, southern Brazil

The redbelly toad Melanophryniscus pachyrhynus (Miranda-Ribeiro, 1920) is a poorly known toad belonging to the M. tumifrons group, which inhabits rocky open areas on top of hilly landscapes of the Uruguayan Savanna ecoregion in Uruguay and southern Brazil. In this study we describe the advertisement and release calls from a redbelly toad population from the central Rio Grande do Sul, southern Brazil, based on recordings obtained during the winter season of 2011. The advertisement call consists of a complex call with two segments, the first segment comprising a series of single, unpulsed notes, and the second comprising a multi-pulsed note (a trill) highly variable in duration. The mean dominant frequency of the call is 2668 ± 154 Hz (2261–2932 Hz) and mean call duration is 37.07 ± 23.97 s (6.64–75.20 s). This feature, however, is highly variable depending on the duration of the second segment, which may be notably longer compared to calls of other species of the genus Melanophryniscus . The release call was recorded during amplexus of up to four individuals. It consists of a short trill with a dominant frequency of approximately 2245 Hz, emitted as a series of five to six pulsed notes, each comprising five or six pulses. The advertisement call of Melanophryniscus pachyrhynus is compared with those of four other Melanophryniscus species, and the similarities in habitat requirements and in the temporal pattern of reproduction for species of the M. tumifrons group are discussed .

Reproduction of deep-sea reef-building corals from the southwestern Atlantic

The logistics of research on deep-sea organisms imposes restrictions on studies that require repetitive long-term collections. Studies on the reproduction of deep-water corals have commonly been made without appropriate temporal series. This study included Madrepora oculata, Solenosmilia variabilis, Lophelia pertusa, and Enallopsammia rostrata, which are among the primary deep-sea reef building corals off Brazil. Samples were collected during 13 consecutive months by the Campos Basin Deep-Sea Corals Assessment Project (R&D Center of the Brazilian Energy Company, Petrobras) in Campos Basin (CB) off Rio de Janeiro State through a remotely-operated-vehicle at approximately 600m depth. Of every monthly sampling campaign, an average of four to five colonies of all four species were investigated histologically. Colonies of both sexes were observed, indicating that all four species are gonochoric. For now, this appears to be the predominant reproductive pattern observed in corals in the area, as well as in deep-sea corals in general, where 80% of coral species are gonochoric. Although considered functionally gonochoric, M. oculata and L. pertusa presented a few colonies with different hermaphroditism patterns. E. rostrata and M. oculata presented continuous reproduction. Although fertile year-round, S. variabilis presents a reproductive peak between April and September (Autumn–Spring) in contrast with the seasonal reproduction recorded in the southwestern Pacific. L. pertusa had a seasonal reproductive peak, confirming previous observations of periodic reproduction in this species in the northeastern Atlantic. The possible spawning season of L. pertusa from CB concentrates between May and July (high frequency of mature gametes), while spawning occurs between January and March in the North Atlantic and between September and November in the Gulf of Mexico. Our results suggest that the studied species are broadcast spawners because no embryos or larvae were observed in any examined sample. This study, based on long-term sampling, provides the most complete data to date on the gametogenesis and temporal patterns of reproduction of four key deep-sea coral reef builder species.

Reproductive Timing in Marine Fishes: Variability, Temporal Scales, and Methods

AbstractReproductive timing can be defined as the temporal pattern of reproduction over a lifetime. Although reproductive timing is highly variable in marine fishes, certain traits are universal, including sexual maturity, undergoing one or more reproductive cycles, participating in one or more spawning events within a reproductive cycle, release of eggs or offspring, aging, and death. These traits commonly occur at four temporal scales: lifetime, annual, intraseasonal, and diel. It has long been known that reproductive timing affects reproductive success, especially in terms of the onset of sexual maturity and the match or mismatch between seasonal spawning and offspring survival. However, a comprehensive understanding of variability in reproductive timing over species, populations, and temporal scales is lacking. In addition, there is a need to assess how variability in reproductive timing affects a population's resilience. Because natural selection occurs at the individual level, this necessitates an understanding of within‐population (i.e., individual) variability in reproductive timing and how fishing may impact it through age truncation and size‐specific selectivity or fisheries‐induced evolution. In this paper, we review the temporal aspects of reproductive strategies and the four most‐studied reproductive timing characteristics in fishes: sexual maturity, spawning seasonality, spawning frequency, and diel periodicity. For each characteristic, we synthesize how it has traditionally been measured, advances in understanding the underlying physiology, its role in equilibrium‐based fish population dynamics, and its importance to reproductive success. We then provide a review of emerging methodology—with an emphasis on ovarian histology—to improve our ability to assess variability in reproductive timing both among populations and within populations.

Seasonality in reproduction, age structure and density of the gracile mouse opossum Gracilinanus microtarsus (Marsupialia: Didelphidae) in a Brazilian cerrado

The temporal pattern of reproduction and its consequences for age structure and density were investigated in a population of the gracile mouse opossum Gracilinanus microtarsus in south-eastern Brazil. Individuals of G. microtarsus were monitored through capture–mark–recapture methods from August 2000 to February 2003 in a remnant of cerradão, a forest-like physiognomy of the highly seasonal cerrado biome. The temporal pattern of reproduction of the population studied was highly seasonal with rearing of the offspring occurring in the first half of the warm-wet season, when the abundance of food resources – primarily insects – in the cerrado is high. Shortly after reproduction, the density of adults decreased sharply, possibly because of high post-mating mortality, leading to a gradual replacement of adults by their offspring in the following months and little overlap of generations. Our data suggest that climatic and environmental factors affect the onset of reproduction and interact with endogenous factors that decrease post-mating survival to produce the observed pattern of seasonal variation in age structure and density. It is suggested that the dynamics of populations of G. microtarsus may be driven primarily by food limitation and that long-term studies are needed to understand its feedback structure.

Reproductive patterns of Trachycephalus venulosus (Laurenti, 1768) and Scinax fuscovarius (Lutz, 1925) from the Cerrado, Central Brazil

Animal mating systems are moulded by ecological factors, mainly the temporal patterns of reproduction. We report the reproductive period, use of microhabitats, clutch and egg sizes, reproductive efforts, occurrence of sexual size dimorphism, and the relation between body size and fecundity in the gravid females of Trachycephalus venulosus and Scinax fuscovarius at Serra da Bodoquena, Central Brazil. The reproduction of both species was correlated with the rainy season. Females of T. venulosus produced more eggs and their eggs were larger than those of S. fuscovarius. The females of both species were larger and heavier than males. The reproductive effort was measured as the ratio of gonad mass in relation to body mass. Females of both species presented similar reproductive efforts, but males of S. fuscovarius invested more in gonads compared to males of T. venulosus. Trachycephalus venulosus presented significant correlation between snout–vent length versus number of mature eggs and body mass versus number of mature eggs and ovarian mass. Scinax fuscovarius showed significant correlation between body mass versus ovarian mass. Trachycephalus venulosus is an explosive breeder, whereas S. fuscovarius has prolonged reproduction. These species are able to adapt to several types of habitat, due to behavioural and physiological plasticity.

How do multiple environmental cycles in combination determine reproductive timing in marine organisms? A model and test

Summary Each of the multiple environmental cycles – the light–dark, tidal, semilunar, lunar and seasonal cycles – may have an independent, specific effect on reproductive timings of marine organisms and can alone or in combination produce a variety of temporal reproductive patterns. Assuming that each ecological interaction with these fluctuating environmental cycles generates a unique functional relationship between a component of fitness and the timing of reproduction, a model is proposed that predicts that all fitness components are multiplicative and therefore the reproductive timing is entrained or driven by a cycle(s) having a sharp functional curve of the relevant fitness component. According to this model, many of the reproductive patterns, ranging from diel to lunar, commonly seen in marine organisms were explained by changing relative kurtosis among functional curves of fitness components. Each curve could also differ in its optimum and skewness, making various intermediates and modifications possible. As a model system for the model to be applied, intraspecific variation in the timing of spawning by a puffer, Takifugu niphobles (Jordan & Snyder) was examined. The patterns of daily variation in a day's spawning time within a population and geographical variation in spawning days among populations indicated that (1) the semilunar cycle (i.e. spring–neap tide cycle) has no direct influence on spawning days, (2) a combination between the functional curves of the fitness components associated with the light–dark and tidal cycles produce an apparent biweekly, semilunar spawning rhythm, (3) the curves may be skewed toward earlier and later times, respectively, and (4) their form may differ among populations. This model approach argues that to understand the ecology and evolution of temporal patterns of reproduction, one must properly decouple and evaluate the form of the functional curve of a fitness component associated with each of the multiple environmental cycles.

SETTLEMENT AND UPSTREAM MIGRATION FOR JAPANESE MITTEN CRAB AND FUNCTION OF SESERAGI-FISHWAY IN NAGARA ESTUARY BARRAGE

Settlement and upstream migration in the Japanese mitten crab (Eriocheir japonica) was investigated in the Seseragi-fishway in the Nagara estuary barrage. Megalopa larvae settled and metamorphosed to crab stage in the upper tidal zone in the Seseragi-fishway. The youngest crabs were nearly two millimeters in carapace width. After attaining a minimum of four millimeters, the crabs began to migrate upstream and reach the freshwater area. Settlement of megalopa larvae occurred mainly in early summer (June) and early winter (December). Their upstream migration to the freshwater area began in July and August. The majority of larvae that settled in winter did not survive and metamorphose to the crab stage due to low water temperatures. Thus, the growth and upstream migration of the Japanese mitten crab seemed to be strongly influenced by water temperature in the estuary. This mode of settlement with two peaks in summer and early winter reflected the temporal pattern of reproduction observed in the sea. In this study, it is clarified that the Seseragi-fishway have a function of settlement and upstream migration for supplement of decreased estuary zone. With respect to engineering works in estuaries such as the Seseragi-fishway, it is recommended that we take into account the processes of settlement and migration of young crabs.