The pipefish brood pouch presents a unique mode of parental care that enables males to protect, osmoregulate, nourish and oxygenate the developing young. Using a very fine O2 probe, we assessed the ...extent to which males of the broad-nosed pipefish (Syngnathus typhle) oxygenate the developing embryos and are able to maintain pouch fluid O2 levels when brooding in normoxia (100% O2 saturation) and hypoxia (40% O2 saturation) for 24 days. In both treatments, pouch fluid O2 saturation levels were lower compared with the surrounding water and decreased throughout the brooding period, reflecting greater offspring demand for O2 during development and/or decreasing paternal ability to provide O2 to the embryos. Male condition (hepatosomatic index) was negatively affected by hypoxia. Larger males had higher pouch fluid O2 saturation levels compared with smaller males, and levels were higher in the bottom section of the pouch compared with other sections. Embryo size was positively correlated with O2 availability, irrespective of their position in the pouch. Two important conclusions can be drawn from our findings. First, our results highlight a potential limitation to brooding within the pouch and dismiss the notion of closed brood pouches as well-oxygenated structures promoting the evolution of larger eggs in syngnathids. Second, we provide direct evidence that paternal care improves with male size in this species. This finding offers an explanation for the documented strong female preference for larger partners because, in terms of oxygenation, the brood pouch can restrict embryo growth.
In species with alternative reproductive tactics, there is much empirical support that parasitically spawning males have larger testes and greater sperm numbers as an evolved response to a higher ...degree of sperm competition, but support for higher sperm performance (motility, longevity and speed) by such males is inconsistent. We used the sand goby (Pomatoschistus minutus) to test whether sperm performance differed between breeding‐coloured males (small testes, large mucus‐filled sperm‐duct glands; build nests lined with sperm‐containing mucus, provide care) and parasitic sneaker‐morph males (no breeding colouration, large testes, rudimentary sperm‐duct glands; no nest, no care). We compared motility (per cent motile sperm), velocity, longevity of sperm, gene expression of testes and sperm morphometrics between the two morphs. We also tested if sperm‐duct gland contents affected sperm performance. We found a clear difference in gene expression of testes between the male morphs with 109 transcripts differentially expressed between the morphs. Notably, several mucin genes were upregulated in breeding‐coloured males and two ATP‐related genes were upregulated in sneaker‐morph males. There was a partial evidence of higher sperm velocity in sneaker‐morph males, but no difference in sperm motility. Presence of sperm‐duct gland contents significantly increased sperm velocity, and nonsignificantly tended to increase sperm motility, but equally so for the two morphs. The sand goby has remarkably long‐lived sperm, with only small or no decline in motility and velocity over time (5 min vs. 22 h), but again, this was equally true for both morphs. Sperm length (head, flagella, total and flagella‐to‐head ratio) did not differ between morphs and did not correlate with sperm velocity for either morph. Thus, other than a clear difference in testes gene expression, we found only modest differences between the two male morphs, confirming previous findings that increased sperm performance as an adaptation to sperm competition is not a primary target of evolution.
Species invasions are a global problem of increasing concern, especially in highly connected aquatic environments. Despite this, salinity conditions can pose physiological barriers to their spread, ...and understanding them is important for management. In Scandinavia's largest cargo port, the invasive round goby (Neogobius melanostomus) is established across a steep salinity gradient. We used 12,937 SNPs to identify the genetic origin and diversity of three sites along the salinity gradient and round goby from western, central and northern Baltic Sea, as well as north European rivers. Fish from two sites from the extreme ends of the gradient were also acclimated to freshwater and seawater, and tested for respiratory and osmoregulatory physiology. Fish from the high‐salinity environment in the outer port showed higher genetic diversity, and closer relatedness to the other regions, compared to fish from lower salinity upstream the river. Fish from the high‐salinity site also had higher maximum metabolic rate, fewer blood cells and lower blood Ca2+. Despite these genotypic and phenotypic differences, salinity acclimation affected fish from both sites in the same way: seawater increased the blood osmolality and Na+ levels, and freshwater increased the levels of the stress hormone cortisol. Our results show genotypic and phenotypic differences over short spatial scales across this steep salinity gradient. These patterns of the physiologically robust round goby are likely driven by multiple introductions into the high‐salinity site, and a process of sorting, likely based on behaviour or selection, along the gradient. This euryhaline fish risks spreading from this area, and seascape genomics and phenotypic characterization can inform management strategies even within an area as small as a coastal harbour inlet.
The Centre for Marine Evolutionary Biology (CeMEB) at the University of Gothenburg, Sweden, was established in 2008 through a 10‐year research grant of 8.7 m€ to a team of senior researchers. Today, ...CeMEB members have contributed >500 scientific publications, 30 PhD theses and have organised 75 meetings and courses, including 18 three‐day meetings and four conferences. What are the footprints of CeMEB, and how will the centre continue to play a national and international role as an important node of marine evolutionary research? In this perspective article, we first look back over the 10 years of CeMEB activities and briefly survey some of the many achievements of CeMEB. We furthermore compare the initial goals, as formulated in the grant application, with what has been achieved, and discuss challenges and milestones along the way. Finally, we bring forward some general lessons that can be learnt from a research funding of this type, and we also look ahead, discussing how CeMEB’s achievements and lessons can be used as a springboard to the future of marine evolutionary biology.
Male alternative reproductive tactics, like satellite or sneaking tactics, typically parasitize reproductively on a larger resource-holding tactic. In the sand goby, Pomatoschistus minutus, 2 types ...of sneaker males are known. Sneaker males with melanization, a typical male breeding coloration, have small testes and large sperm-duct glands, and sneaker males without melanization have large testes and small sperm-duct glands. We tested their potential to change into the nest-holding tactic experimentally by keeping them with or without a large nest-holding male. With nest-holding males, neither sneaker male type built nests. However, without nest-holding males, a large proportion of both types of sneaker males built nests and became nest-holders, and all the nest-building nonmelanized sneaker males developed melanization. Furthermore, nest-building nonmelanized sneaker males had larger sperm-duct glands (used to produce a sperm-containing mucus) than nonnest-building nonmelanized sneaker males. However, contrary to our expectation, treatment did not affect testes size. Compared with melanized sneaker males nonmelanized sneaker males tended to have a lower proportion of nest-building males and showed significantly less reproductive activity, especially in the early experimental period. Finally, in a separate experiment, we confirmed that nonmelanized sneaker males that build nests can spawn and tend eggs normally. Taken together, our results suggest that these tactics are not genetically or ontogenetically fixed but condition dependent. However, this does not exclude an underlying genetic variation in phenotype expression.
Genetic monogamy is the rule for many species of seahorse, including the West Australian seahorse
Hippocampus subelongatus
. In this paper, we revisit mark-recapture and genetic data of
H. ...subelongatus
, allowing a detailed characterization of movement distances, home range sizes and home range overlaps for each individual of known sex, paired status (paired or unpaired) and body size. As predicted, we find that females have larger home ranges and move greater distances compared to males. We also confirm our prediction that the home ranges of pair-bonded individuals (members of a pair known to reproduce together) overlap more on average than home ranges of randomly chosen individuals of the opposite or same sex. Both sexes, regardless of paired status, had home ranges that overlapped with, on average, 6–10 opposite-sex individuals. The average overlap area among female home ranges was significantly larger than the overlap among male home ranges, probably reflecting females having larger home ranges combined with a female biased adult sex ratio. Despite a prediction that unpaired individuals would need to move around to find a mate, we find no evidence that unpaired members of either sex moved more than paired individuals of the same sex. We also find no effect of body size on home range size, distance moved or number of other individuals with which a home range overlapped. These patterns of movement and overlap in home ranges among individuals of both sexes suggest that low mate availability is not a likely explanation for the maintenance of monogamy in the West Australian seahorse.
In animals, colorful and conspicuous ornaments enhance individual attractiveness to potential mates, but are typically tempered by natural selection for crypsis and predator protection. In species ...where males compete for females, this can lead to highly ornamented males competing for mating opportunities with choosy females, and vice versa. However, even where males compete for mating opportunities, females may exhibit conspicuous displays. These female displays are often poorly understood and it may be unclear whether they declare mating intent, signal intrasexual aggression or form a target for male mate preference. We examined the function of the conspicuous dark eyes that female sand gobies temporarily display during courtship by experimentally testing if males preferred to associate with females with artificially darkened eyes and if dark eyes are displayed during female aggression. By observing interactions between a male and two females freely associating in an aquarium we also investigated in which context females naturally displayed dark eyes. We found that dark eyes were more likely to be displayed by more gravid females than less gravid females and possibly ahead of spawning, but that males did not respond behaviorally to dark eyes or prefer dark-eyed females. Females behaving aggressively did not display dark eyes. We suggest that dark eyes are not a signal per se but may be an aspect of female mate choice, possibly related to vision.
In sexually reproducing animals, individuals of one sex may have to compete for access to mating partners of the opposite sex. The operational sex ratio (OSR) is central in predicting the intensity ...of mating competition and which sex is competing for which. Thanks to recent theoretical and empirical advances, particularly by exploring the concept of OSR, sexual selection studies today are becoming more fine-tuned and dynamic. The original role of parental investment in predicting sexual selection has recently been complemented by the use of sexual differences in potential reproductive rates (PRR).
Endless forms of sexual selection Lindsay, Willow R; Andersson, Staffan; Bererhi, Badreddine ...
PeerJ (San Francisco, CA),
11/2019, Letnik:
7
Journal Article
Recenzirano
Odprti dostop
In recent years, the field of sexual selection has exploded, with advances in theoretical and empirical research complementing each other in exciting ways. This perspective piece is the product of a ...“stock-taking” workshop on sexual selection and sexual conflict. Our aim is to identify and deliberate on outstanding questions and to stimulate discussion rather than provide a comprehensive overview of the entire field. These questions are organized into four thematic sections we deem essential to the field. First we focus on the evolution of mate choice and mating systems. Variation in mate quality can generate both competition and choice in the opposite sex, with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems, especially with regard to polyandry. Second, we focus on how sender and receiver mechanisms shape signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are challenging to measure. We view the neuroethology of sensory and cognitive receiver biases as the main key to signal form and the ‘aesthetic sense’ proposed by Darwin. Since a receiver bias is sufficient to both initiate and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate ‘null model’ of sexual selection. Thirdly, we focus on the genetic architecture of sexually selected traits. Despite advances in modern molecular techniques, the number and identity of genes underlying performance, display and secondary sexual traits remains largely unknown. In-depth investigations into the genetic basis of sexual dimorphism in the context of long-term field studies will reveal constraints and trajectories of sexually selected trait evolution. Finally, we focus on sexual selection and conflict as drivers of speciation. Population divergence and speciation are often influenced by an interplay between sexual and natural selection. The extent to which sexual selection promotes or counteracts population divergence may vary depending on the genetic architecture of traits as well as the covariance between mating competition and local adaptation. Additionally, post-copulatory processes, such as selection against heterospecific sperm, may influence the importance of sexual selection in speciation. We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection, and we offer potential avenues of research to advance this progress.
The operational sex ratio (OSR, ready-to-mate males to females) is a key factor determining mating competition. A shortage of a resource essential for reproduction of one sex can affect OSR and lead ...to competition within the opposite sex for resource-holding mates. In the sand goby (
Pomatoschistus minutus
), a fish with paternal care, male readiness to mate depends on acquiring a nest-site, whereas food abundance primarily impacts female egg production. Comparing body condition and gonadal investment of fish from two populations with different availability in resources (Baltic Sea: few nest-sites, more food; North Sea: many nest-sites, less food), we predicted females carrying more mature eggs in the Baltic Sea than in the North Sea. As predicted, ovaries were larger in Baltic Sea females, and so was the liver (storage of energy reserves and vitellogenic compounds) for both sexes, but particularly for females. More females were judged (based on roundness scores) to be ready to spawn in the Baltic Sea. Together with a nest colonization experiment confirming a previously documented difference between the two areas in nest-site availability, these results indicate a more female-biased OSR in the Baltic Sea population, compared to the North Sea, and generates a prediction that female–female competition for mating opportunities is stronger in the Baltic population. To our knowledge, this is the first time that female reproductive investment is discussed in relation to OSR using field data.
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