Differences In Reproductive Timing Research Articles

Genome-wide SNP analysis coupled with geographic and reproductive-phenological information reveals panmixia in a classical marine species, the Japanese jack mackerel (Trachurus japonicus)

Identification of genetic population structures in classical marine species—species with large population sizes, wide range distributions, and high dispersal potential—can be a challenging task because of expectedly weak genetic signals of population structure. The Japanese jack mackerel, Trachurus japonicus, is a classical marine species and one of the most important fishery resources in the East Asian seas. In this study, we tested the hypothesis of genetic panmixia in the Japanese jack mackerel using genome-wide SNP analyses coupled with geographic and reproductive phenology information. We generated a highly contiguous genome assembly and performed Genotyping by Random Amplicon Sequencing-Direct (GRAS-Di) to produce at least 19,904 SNPs that were genotyped in 614 samples from seas around the Japanese archipelago. Genetic population structure analyses did not reveal any evidence of genetic differentiation. Neither geographical barriers in the Japanese archipelago nor phenological differences in reproductive timing affected the genetic population structure. Overall, these findings were consistent with the interpretation of genetic panmixia, providing evidence for high genetic connectivity across the population’s distribution. Considering the current knowledge about the distribution and life history of T. japonicus, we suggest that the panmictic status may reflect a metapopulation structure with source-sink dynamics and/or extensive gene flow across the distribution range.

Effective Techniques for the Feeding and <em>Ex Situ</em> Culture of a Brooding Scleractinian Coral, <em>Pocillopora acuta</em>

Climate change is affecting the survival, growth, and recruitment of corals globally, with large-scale shifts in abundance and community composition expected in reef ecosystems over the next several decades. Recognition of this reef degradation has prompted a range of novel research- and restoration-based active interventions. Ex situ aquaculture can play a supporting role through the establishment of robust coral culture protocols (e.g., to improve health and reproduction in long-term experiments) and through the provision of a consistent broodstock supply (e.g., for use in restoration projects). Here, simple techniques for the feeding and ex situ culture of brooding scleractinian corals are outlined using the common and well-studied coral, Pocillopora acuta, as an example. To demonstrate this approach, coral colonies were exposed to different temperatures (24 °C vs. 28 °C) and feeding treatments (fed vs. unfed) and the reproductive output and timing, as well as the feasibility of feeding Artemia nauplii to corals at both temperatures, was compared. Reproductive output showed high variation across colonies, with differing trends observed between the temperature treatments; at 24 °C, fed colonies produced more larvae than unfed colonies, but the opposite was found in colonies cultured at 28 °C. All colonies reproduced before the full moon, and differences in reproductive timing were only found between unfed colonies in the 28 °C treatment and fed colonies in the 24 °C treatment (mean lunar day of reproduction ± standard deviation: 6.5 ± 2.5 and 11.1 ± 2.6, respectively). The coral colonies fed efficiently on Artemia nauplii at both treatment temperatures. These proposed feeding and culture techniques focus on the reduction of coral stress and the promotion of reproductive longevity in a cost-effective and customizable manner, with versatile applicability in both flow-through and recirculating aquaculture systems.

Size‐associated energetic constraints on the seasonal onset of reproduction in a species with indeterminate growth

The seasonal onset of reproduction is constrained in many systems by a need to first accumulate energetic reserves. Consequently, the observation that larger individuals reproduce earlier may be due to a negative relationship between size and mass‐specific basal metabolic rate that is shared across diverse taxa. However, an untested prediction of this hypothesis is that individuals should be metabolically efficient enough to escape energetic constraints above a certain size threshold. Seasonally reproducing species, such as temperate fishes, that must recover winter energy losses before reproduction and exhibit indeterminate growth are ideal models to test this prediction. We harness decade‐long behavioral data on parental male smallmouth bass, Micropterus dolomieu, to investigate contributions of energetic allometry to differences in reproductive timing. At the population level, peak seasonal reproductive timing (i.e. the median date on which eggs were found in nests each year) was negatively related to degree days – a measure of thermal energy experienced – before reproduction. At the individual level, degree days accumulated by males before reproduction was related to male size and condition in every year, but the impact of temperature on reproductive timing by the largest males was relaxed in most years. Additionally, we used our data to replicate the analyses of two previous studies of M. dolomieu populations and found virtually identical negative associations between male body size and degree days accumulated before reproduction. Our results suggest that in smallmouth bass the onset of seasonal reproduction is constrained by basal metabolic rate – as indicated by total length – and that large individuals can escape size‐associated energetic constraints. We reveal a more complicated relationship between size and reproductive timing than earlier studies, which may be relevant for many species. Knowledge of this relationship is critical to understanding how a changing climate will influence population dynamics of economically, ecologically and recreationally important species like M. dolomieu.

Temperature-associated selection linked to putative chromosomal inversions in king scallop (Pecten maximus).

The genomic landscape of divergence—the distribution of differences among populations or species across the genome—is increasingly characterized to understand the role that microevolutionary forces such as natural selection and recombination play in causing and maintaining genetic divergence. This line of inquiry has also revealed chromosome structure variation to be an important factor shaping the landscape of adaptive genetic variation. Owing to a high prevalence of chromosome structure variation and the strong pressure for local adaptation necessitated by their sessile nature, bivalve molluscs are an ideal taxon for exploring the relationship between chromosome structure variation and local adaptation. Here, we report a population genomic survey of king scallop (Pecten maximus) across its natural range in the northeastern Atlantic Ocean, using a recent chromosome-level genome assembly. We report the presence of at least three large (12–22 Mb), putative chromosomal inversions associated with sea surface temperature and whose frequencies are in contrast to neutral population structure. These results highlight a potentially large role for recombination-suppressing chromosomal inversions in local adaptation and suggest a hypothesis to explain the maintenance of differences in reproductive timing found at relatively small spatial scales across king scallop populations.

Phenological displacement is uncommon among sympatric angiosperms

Interactions between species can influence successful reproduction, resulting in reproductive character displacement, where the similarity of reproductive traits - such as flowering time - among close relatives growing together differ from when growing apart. Evidence for the overall prevalence and direction of this phenomenon, and its stability under environmental change, remains untested across large scales. Using the power of crowdsourcing, we gathered phenological information from over 40 000 herbarium specimens, and investigated displacement in flowering time across 110 animal-pollinated species in the eastern USA. Overall, flowering time displacement is not common across large scales. However, displacement is generally greater among species pairs that flower close in time, regardless of direction. Furthermore, with climate change, the flowering times of closely related species are predicted, on average, to shift further apart by the mid-21st century. We demonstrate that the degree and direction of phenological displacement among co-occurring closely related species pairs varies tremendously. However, future climate change may alter the differences in reproductive timing among many of these species pairs, which may have significant consequences for species interactions and gene flow. Our study provides one promising path towards understanding how the phenological landscape is structured and may respond to future environmental change.

Fine-scale morphological, genomic, reproductive, and symbiont differences delimit the Caribbean octocorals Plexaura homomalla and P. kükenthali

Octocorals are conspicuous members of coral reefs and deep-sea ecosystems. Yet, species boundaries and taxonomic relationships within this group remain poorly understood, hindering our understanding of this essential component of the marine fauna. We used a multifaceted approach to revisit the systematics of the Caribbean octocorals Plexaura homomalla and Plexaura kükenthali, two taxa that have a long history of taxonomic revisions. We integrated morphological and reproductive analyses with high-throughput sequencing technology to clarify the relationship between these common gorgonians. Although size and shape of the sclerites are significantly different, there is overlap in the distributions making identification based on sclerites alone difficult. Differences in reproductive timing and mode of larval development were detected, suggesting possible mechanisms of pre-zygotic isolation. Furthermore, there are substantial genetic differences and clear separation of the two species in nuclear introns and single-nucleotide polymorphisms obtained from de novo assembled transcriptomes. Despite these differences, analyses with SNPs suggest that hybridization is still possible between the two groups. The two nascent species also differed in their symbiont communities (genus Breviolum) across multiple sampling sites in the Caribbean. Despite a complicated history of taxonomic revisions, our results support the differentiation of P. homomalla and P. kükenthali, emphasizing that integrative approaches are essential for Anthozoan systematics.

Intra‐population variation in reproductive timing covaries with thermal plasticity of offspring performance in perch Percafluviatilis

Life history theory posits that organisms should time their reproduction to coincide with environmental conditions that maximize their fitness. Population-level comparisons have contributed important insights on the adaptive value of reproductive timing and its association to environmental variation. Yet, despite its central role to ecology and evolution, the causes and consequences of variation in reproductive timing among individuals within populations are poorly understood in vertebrates other than birds. Using a combination of observational field studies and a split-brood experiment, we investigated whether differences in breeding time were associated with changes in hatching success, reproductive allocation and reaction norms linking offspring performance to temperature within an anadromous Baltic Sea population of perch Perca fluviatilis. Field observations revealed substantial variation in reproductive timing, with the breeding period lasting almost 2months and occurring in temperatures ranging from 10 to 21℃. The hatching success of perch decreased as the reproductive season progressed. At the same time, the reproductive allocation strategy changed over the season, late breeders (the offspring of which were introduced into a high resource environment and increased predation pressure) produced more and smaller eggs that resulted in smaller larvae, compared with early breeders. The split-brood experiment in which eggs were incubated in different temperatures (10, 12, 15, 18°C) showed that differences in reproductive timing were associated with a change in the shape of the reaction norm linking offspring performance to water temperature indicative of adaptive phenotypic plasticity, with the offspring of early breeders performing best in low temperatures and the offspring of late breeders performing best in high temperatures. The seasonal changes in reproductive traits and the shape of the thermal performance suggest time-dependent adaptive differences among individuals within the population. Management actions aimed at preserving and restoring variation in the timing of reproductive events will thus likely also influence variation in associated life history traits and thermal performance curves, which could safeguard populations against environmental challenges and changes associated with exploitation and global warming.

Migrant and resident female songbirds differ in gonadal response to upstream stimulation during seasonal sympatry

Timing of seasonal reproduction is driven by environmental cues acting on the hypothalamic-pituitary–gonadal (HPG) axis. Groups of individuals, or populations, of the same species can exhibit different phenology despite facing similar environmental cues or living in the same habitat (i.e., seasonal sympatry). The mechanisms giving rise to population-level differences in reproductive timing are not fully understood, particularly for females. We studied the dark-eyed junco, a songbird with migratory and sedentary (i.e., resident) populations that live in overlapping distributions during winter. In early spring, residents initiate breeding and associated behaviors, including territory establishment and formation of pair bonds, while migrants prepare to depart for their breeding grounds. We tested whether migrant and resident hormonal response to upstream hormonal stimulation differed during this time period. We collected blood from free-living females in early spring, and challenged them with repeated gonadotropin-releasing hormone (GnRH) injections to measure testosterone (T) response. We predicted that if migrants are less sensitive to upstream stimulation than residents, then they would exhibit lower response to the repeated GnRH challenges in migrants. We found that migrant and resident females both responded to an initial challenge by elevating T, but residents responded more robustly, indicating that the ovary plays a role in population-level differences in reproductive timing. We also found that migrants and residents attenuated their response to repeated challenges, and did not differ from one another in final T levels. We speculate that the explanation for the generally reduced T response after repeated GnRH injections need not be the same for migrants and residents, but possible explanations include suppression of upstream stimulation owing to negative feedback after the initial injection oraromatization of T to estradiol between sampling time points. We suggest that future studies experimentally explore how the ovarian response to upstream stimulation changes during the transition to reproduction.

Identifying Life-History Traits That Promote Occurrence for Four Minnow (Leuciscidae) Species in Intermittent Gulf Coastal Plain Streams

Life-history traits of stream fishes partly reflect adaptations to disturbance regimes, which in turn shape assemblage composition via environmental filters. In this study, we focused on life-history traits of 4 morphologically similar leuciscid species in coastal plain streams of southwestern GA that are shifting from historically perennial to intermittent flow. We evaluated the following traits hypothesized to influence species persistence in intermittent streams: differences in reproductive timing, sex ratio, body size at maturity, reproductive investment, and diet. First, we ordinated published species occurrence data for samples of fish communities in perennial and intermittent streams in the study region, and identified 4 focal taxa as differing in their associations with intermittency. We then periodically sampled individuals of the focal taxa in 14 streams over a year (May 2016–April 2017). We found that for Pteronotropis harperi (Redeye Chub), a species strongly associated with intermittent streams, reproductive timing did not overlap with typical seasonal stream drying. Redeye Chub also had the significantly smallest minimum length at maturation and the greatest reproductive investment. Fishes associated with perennial streams (Pteronotropis grandipinnis [Apalachee Shiner] and Notropis texanus [Weed Shiner]), or not associated with either stream type (Notropis petersoni [Coastal Shiner]), had at least a portion of their reproductive timing overlapping with times when streams were likely to dry, and had similar and significantly lower reproductive investment than Redeye Chub. Redeye Chub displayed no shift in diet when streams ceased flowing, while Apalachee Shiner showed decreases in terrestrial prey. Our results suggest that size at maturity, reproductive timing, and reproductive investment may promote persistence by the Redeye Chub given projections of more frequent and intense periods of stream intermittency.

Seasonally sympatric songbirds that differ in migratory strategy also differ in neuroendocrine measures

Seasonally breeding animals initiate gonadal recrudescence when mechanisms that suppress reproduction give way to mechanisms that stimulate it. However, knowledge of mechanistic changes in hormonal regulation during this transition is limited. Further, most studies of reproductive timing have focused on males, despite the critical role of females in determining breeding phenology. Closely related populations that live in the same environment but differ in reproductive timing provide an opportunity to examine differences in mechanisms during the transition from the pre-reproductive to reproductive state. We studied closely related migrant and resident populations of dark-eyed juncos (Junco hyemalis) that reside in the same environment in spring but differ in breeding phenology. Residents initiate breeding earlier than migrants, which do not breed until after they have migrated. To directly study differences in the hypothalamic mechanisms of reproduction, we captured 16 migrant and 13 resident females from the field on March 25-April 11. We quantified expression of mRNA transcripts and show that resident females had higher abundance of gonadotropin-releasing hormone transcripts than migrant females, indicating greater reproductive development in resident than migrant females living in the same environment. We also found higher transcript abundance of estrogen receptor and androgen receptor in migrant than resident females, suggesting that negative feedback may delay reproductive development in migrant females until after they migrate. These differences in hypothalamic mechanisms may help to explain differences in reproductive timing in populations that differ in migratory strategy.

Migratory strategy explains differences in timing of female reproductive development in seasonally sympatric songbirds

Abstract Divergent migratory strategies among populations can result in population‐level differences in timing of reproduction (allochrony) and local adaptation. However, the mechanisms underlying among‐population variation in timing are insufficiently understood, particularly in females. We studied differences in reproductive development and its related mechanisms along the hypothalamic–pituitary–gonadal axis (HPG) in closely related migratory and sedentary (i.e. resident) female dark‐eyed juncos (Junco hyemalis) living together in sympatry during early spring. Despite exposure to the same environmental cues in early spring, residents initiate breeding prior to the departure of migrants for their breeding grounds. We investigated whether residents would be more reproductively developed than migrants based on their behavioural differences. Alternatively, females could exhibit similar reproductive development in response to the same environmental cues despite differences in migratory behaviour. To compare their degree of reproductive development during seasonal sympatry and the underlying mechanisms of these differences, we collected ovarian and liver tissue in early spring prior to migration and compared transcript abundance of genes associated with reproduction using quantitative PCR. We also used stable hydrogen isotopes to infer relative breeding and wintering latitude of migrants. We found higher transcript abundance of luteinizing hormone receptor and aromatase in the ovary in addition to significantly heavier ovaries in residents than in migrants. Together, these results suggest greater sensitivity and response to upstream endocrine stimulation in resident females. Transcript abundance for other receptors in the ovary and liver associated with reproduction, however, did not differ between populations. When comparing ovarian development within migrants, females with lower hydrogen isotopes (indicating higher breeding latitudes) had smaller ovaries, suggesting that longer‐distance migrations may further delay reproductive development. Based on differences in ovary mass and transcript abundance, we conclude that females that differ in migratory strategy also differ in timing of reproductive development. These results support that divergent migratory behaviour drives allochrony and could enable reproductive isolation between populations; mechanistic differences at the level of gonadal stimulation can explain these differences in timing of reproductive development. A free Plain Language Summary can be found within the Supporting Information of this article.

Male courtship preference during seasonal sympatry may maintain population divergence.

Animal migration can lead to a population distribution known as seasonal sympatry, in which closely‐related migrant and resident populations of the same species co‐occur in sympatry during part of the year, but are otherwise allopatric. During seasonal sympatry in early spring, residents may initiate reproduction before migrants depart, presenting an opportunity for gene flow. Differences in reproductive timing between migrant and resident populations may favor residents that exhibit preferences for potential mates of similar migratory behavior and reproductive timing, thus maintaining population divergence. We studied dark‐eyed juncos (Junco hyemalis), a songbird that exhibits seasonal sympatry. We conducted simulated courtship interactions in which we presented free‐living resident males with either a caged migrant or resident female and quantified courtship behavior prior to the departure of the migrants. We found that resident males preferred to court resident females: they sang more short‐range songs and exhibited more visual displays associated with courtship when presented with resident females. We conclude that males distinguish between migrant and resident females during seasonal sympatry when the risk of interacting with non‐reproductive, migrant females is high. Male mate choice in seasonal sympatry is likely adaptive for male reproductive success. As a secondary effect, male mating preference could act to maintain or promote divergence between populations that differ in migratory strategy.

Consistent differences in fitness traits across multiple generations of Olympia oysters

Adaptive evolution and plasticity are two mechanisms that facilitate phenotypic differences between populations living in different environments. Understanding which mechanism underlies variation in fitness-related traits is a crucial step in designing conservation and restoration management strategies for taxa at risk from anthropogenic stressors. Olympia oysters (Ostrea lurida) have received considerable attention with regard to restoration, however there is limited information on adaptive population structure. Using oysters raised under common conditions for up to two generations (F1s and F2s), we tested for evidence of divergence in reproduction, larval growth, and juvenile growth among three populations in Puget Sound, Washington. We found that the population with the fastest growth rate also exhibited delayed and reduced reproductive activity, indicating a potential adaptive trade-off. Our results corroborate and extend upon a previous reciprocal transplant study on F1 oysters from the same populations, indicating that variation in growth rate and differences in reproductive timing are consistent across both natural and laboratory environments and have a strongly heritable component that cannot be entirely attributed to plasticity.

Relationship Among Plasma Tiglycerides, Body Mass, Reproduction of Northern Bobwhites

The earliest potential initiation of northern bobwhite (Colinus virginianus) reproduction is limited by photoperiod. Secondary factors such as lipid reserves, diet, and stress often limit the beginning of northern bobwhite reproduction, potentially reducing reproductive success and causing a shorter reproductive season. We measured late winter body masses and plasma triglycerides of wild northern bobwhites and subsequent reproductive timing and effort in 1997 and 1998 on the coastal prairie of Texas. Using body mass and plasma triglyceride levels as indices of body fat, we tested the hypothesis that the onset of reproduction and first clutch size was influenced by late winter lipid reserves. Northern bobwhite plasma triglycerides were higher (P < 0.001) and more variable (P = 0.019) in 1998, and nesting began 15 ± 1.6 days (c ± SE) earlier than in 1997. However, within each year, no combination of body mass and triglycerides was associated with timing of nesting or size of first clutch (P > 0.1). In addition, body masses were not correlated with plasma triglycerides (P > 0.1). Our findings suggest that individual plasma triglyceride levels and body mass are unsuitable variables for assessing within-population differences in reproductive timing. However, mean plasma triglycerides for a population may be useful for assessing differences in reproductive timing among years and locations. The relationship between triglycerides and hormones directly affecting gonadal recrudescence, such as luteinizing hormone (LH) and prolactin, is uncertain for wild northern bobwhites. Thus, future studies should assess causes and patterns of change in these hormones.

Phylogenetic analysis of the winter geometrid genus Inurois reveals repeated reproductive season shifts.

Winter geometrid moths belonging to the genus Inurois comprise nine species that reproduce during early winter, three species that reproduce in late winter, and polymorphic species with genetically diverged early and late winter populations that co-occur widely across the species' range. In our previous studies, we demonstrated that differences in reproductive timing resulted in allochronic reproductive isolation between sympatric populations. In the present study, to assess the evolutionary pattern of reproductive timing within the genus, we determined the phylogenetic relationships among species using nuclear and mitochondrial gene sequences. Nuclear gene tree showed that reproductive season shifts occurred independently in four of 13 divergence events. In two divergence events, allochronic sister lineages were formed in sympatry, suggesting that the segregation of the reproductive season was associated with diversification in the genus Inurois. We also found that the mitochondrial gene tree was quite different from the nuclear gene tree and that mitochondrial introgression may have occurred in a few cases. Although it remains unclear whether early and late winter species actually have hybridized with each other and how strong or stable is the reproductive isolation provided by the reproductive season segregation, our study illuminates the potential importance of allochronic isolation in the diversification process of the genus Inurois.

The marginal valuation of fertility

Substantial theoretical and empirical evidence demonstrates that fertility entails economic, physiological, and demographic trade-offs. The existence of trade-offs suggests that fitness should be maximized by an intermediate level of fertility, but this hypothesis has not had much support in the human life-history literature. We suggest that the difficulty of finding intermediate optima may be a function of the way fitness is calculated. Evolutionary analyses of human behavior typically use lifetime reproductive success as their fitness criterion. This fitness measure implicitly assumes that women are indifferent to the timing of reproduction and that they are risk-neutral in their reproductive decision-making. In this paper, we offer an alternative, easily-calculated fitness measure that accounts for differences in reproductive timing and yields clear preferences in the face of risky reproductive decision-making. Using historical demographic data from a genealogically-detailed dataset from 19th century Utah, we show that this measure is highly concave with respect to reproductive effort. This result has three major implications: (1) if births are properly timed, a lower-fertility reproductive strategy can have the same fitness as a high-fertility strategy, (2) intermediate optima are far more likely using fitness measures that are strongly concave with respect to effort, (3) we expect mothers to have strong investment preferences with respect to the risk inherent in reproduction.

Sex-specific hoarding behavior in North American red squirrels (Tamiasciurus hudsonicus)

In short-term hoarding rodents, reproduction and hoarding often overlap and reproductive status can alter hoarding behavior. In long-term hoarders these activities are often separated seasonally. Therefore, annual and sex-specific variation in the timing of reproduction relative to the hoarding season may influence variation in the hoarding behavior of long-term hoarders. North American red squirrels (Tamiasciurus hudsonicus) clip and hoard white spruce (Picea glauca) cones each autumn, but have variation in reproductive timing such that in some years the hoarding season overlaps with reproductive activity. Over 4 years with naturally varying cone availability we quantified reproductive timing and hoarding behavior. Males completed mating 22–90 days before the onset of hoarding, whereas large numbers (45–86%) of females during large cone crop years weaned litters after hoarding commenced. Despite these differences in reproductive timing, across all years females clipped more cones than did males, whereas males hoarded more cones and had a higher propensity to larder-hoard than did females. Interestingly, in the years with large cone crops, females that weaned their litters later (during the hoarding season) did not have reduced hoarding or reproductive performance (offspring growth and recruitment) than females that weaned their litters earlier. In the year with the most extensive overlap between female reproduction and hoarding, lactating females did not differ from males in the amount of time they allocated to hoarding. In this year, the daily energy expenditure of lactating females during the hoarding season did not differ from that of males engaged in hoarding or from that of lactating females prior to the hoarding season. Hence, under high-resource conditions the competing demands of lactation and hoarding can both be sustained, allowing red squirrels flexibility in the separation between reproduction and hoarding.

Chronobiology of seasonal reproduction: Neuroendocrine mechanisms and geographic variation

Event Abstract Back to Event Chronobiology of seasonal reproduction: Neuroendocrine mechanisms and geographic variation Deborah I. Lutterschmidt1* 1 Portland State University, Department of Biology, United States The ability to integrate and respond to changing environmental cues with appropriate physiology and behavior is crucial to the survival and reproductive fitness of all organisms. One of the most critical life history traits subject to environmental control is reproduction. However, the upstream mechanisms governing how the reproductive axis receives and integrates environmental cues are poorly understood. Moreover, temperature may be the primary environmental cue regulating reproduction in ectotherms, yet we know very little about the neuroendocrine mechanisms mediating temperature-induced reproduction. We recently demonstrated that melatonin concentrations of common garter snakes (Thamnophis sirtalis) hibernated at 5°C were significantly lower than those of snakes maintained at 10°C. These temperature-induced differences in melatonin rhythms between treatment groups persisted even after both groups were again acclimated to 10°C, indicating that low temperature exposure has a lasting influence on melatonin rhythms. We further examined whether melatonin rhythms may mediate differences in reproductive timing both between sexes and among populations. Critically, we observed sex differences in melatonin cycles of T. sirtalis during the spring mating season, and these sex differences were present in each of the 3 garter snake populations studied. Whether sexually dimorphic melatonin cycles are related to the expression of male courtship behavior requires further study. We also observed population differences in melatonin cycles across a wide range of acclimatization conditions, and these differences were themselves plastic. Changes in male courtship behavior and androgen concentrations during spring emergence also varied significantly among these populations, despite acclimatization to identical environmental conditions. These data provide support for the hypothesis that melatonin-mediated responses to environmental cues govern differences in reproductive timing. Keywords: courtship behavior, geographic variation, melatonin rhythm, Reproduction, reptile, sex steroid hormones, temperature, winter dormancy Conference: ISAREN 2011: 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology, Ann Arbor, United States, 11 Jul - 13 Jul, 2011. Presentation Type: Invited Symposium Topic: Reproduction Citation: Lutterschmidt DI (2011). Chronobiology of seasonal reproduction: Neuroendocrine mechanisms and geographic variation. Front. Endocrinol. Conference Abstract: ISAREN 2011: 7th International Symposium on Amphibian and Reptilian Endocrinology and Neurobiology. doi: 10.3389/conf.fendo.2011.03.00028 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 20 Jul 2011; Published Online: 09 Aug 2011. * Correspondence: Dr. Deborah I Lutterschmidt, Portland State University, Department of Biology, Portland, OR, 97207, United States, dil@uci.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Deborah I Lutterschmidt Google Deborah I Lutterschmidt Google Scholar Deborah I Lutterschmidt PubMed Deborah I Lutterschmidt Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Clock polymorphism in Pacific salmon: evidence for variable selection along a latitudinal gradient

Seasonal timing of life-history events is often under strong natural selection. The Clock gene is a central component of an endogenous circadian clock that senses changes in photoperiod (day length) and mediates seasonal behaviours. Among Pacific salmonids (Oncorhynchus spp.), seasonal timing of migration and breeding is influenced by photoperiod. To expand a study of 42 North American Chinook salmon (Oncorhynchus tshawytscha) populations, we tested whether duplicated Clock genes contribute to population differences in reproductive timing. Specifically, we examined geographical variation along a similar latitudinal gradient in the polyglutamine domain (PolyQ) of OtsClock1a and OtsClock1b among 53 populations of three species: chum (Oncorhynchus keta), coho (Oncorhynchus kisutch) and pink salmon (Oncorhynchus gorbuscha). We found evidence for variable selection on OtsClock1b that corresponds to latitudinal variation in reproductive timing among these species. We evaluated the contribution of day length and a freshwater migration index to OtsClock1b PolyQ domain variation using regression trees and found that day length at spawning explains much of the variation in OtsClock1b allele frequency among chum and Chinook, but not coho and pink salmon populations. Our findings suggest that OtsClock1b mediates seasonal adaptation and influences geographical variation in reproductive timing in some of these highly migratory species.

Differences in reproductive timing among sponges sharing habitat and thermal regime

Abstract. The reproductive cycles of four Mediterranean demosponges (Axinella damicornis, Corticium candelabrum, Raspaciona aculeata, and Chondrosia reniformis) were investigated during 2 consecutive years. Three of the species had annual gametogenic cycles characterized by a single peak of gamete production, but members of C. candelabrum showed continuous oocyte production during the 2 years. The relationship between gametogenic dynamics and seawater temperature varied substantially among species, contrary to the widespread belief that gamete production is associated with seasonal water warming. The annual temperature increase (in June) concurred with oocyte production only in C. reniformis, although maximum temperatures were simultaneous with the production of both oocytes in R. aculeata and sperm in C. reniformis. In contrast, the annual temperature decline in October was associated with both oogenesis in A. damicornis and spermatogenesis in R. aculeata. Spermatogenesis in A. damicornis started after a 5‐month period of low‐temperature values (December–April in 2004 and November–March in 2005). Likewise, in C. candelabrum, spermatogenesis started after a 3‐month period of low‐temperature values (November–February), a period concomitant with a slow increase in oocyte production. These findings reveal that sponge species that cooccur and share similar thermal regimes may differ substantially in their timing of gamete production. If we are to predict the future effects of climate change on marine benthic communities, there is an urgent need to improve our knowledge of the species‐specific relationship between timing of gametogenesis and temperature, at least for those sponges that are key species in benthic communities.