Disentangling the determinants of reproductive success in a temperate reef fish, Forsterygion lapillum

<p>Identifying sources of individual variation in reproductive success has been a longstanding challenge for evolutionary ecologists. Reproductive success among individuals can be due to several factors such as competition between conspecifics for nest sites and mating partners, mate choice, or by the physical environment. Reproductive success, particularly among males, can be extremely diverse both within and between species and determining which components contribute to success can be particularly challenging. In this thesis, I investigated patterns and drivers of reproductive success in a temperate marine reef fish, Forsterygion lapillum (the common triplefin). Specifically, I examined how male quality, nest quality, and female choice influence male reproductive success. Additionally, I quantified male reproductive success during the winter and summer of the breeding season to examine the temporal dynamics of breeding success in F. lapillum. Selection of mates by females can be driven by the quality and behavioural attributes of the male or by the quality of resources offered. In Chapter 2, using field-based observations, combined with a lab-based study, I evaluated the effects of different male traits and nest characteristics on female choice and male reproductive success. Specifically, I observed egg guarding males in the field during the breeding season and recorded their phenotypic traits, behaviours, and nest characteristics. I then examined their influence on 3 different components of male reproductive success (brood size, individual egg size, and mate attraction). Additionally, I conducted dichotomous choice tests in the laboratory to evaluate female preference for different sized males, holding different sized nests. In the field, I did not detect a significant relationship between male mating success and male total length or nest size. Brood size and individual egg size were highly variable among sampled males, however, further factors such as courtship frequency, and the number of interactions with potential predators did not explain any additional variation. The number of agonistic displays performed by egg guarding males was the only factor to influence egg size, however, it had no direct impact on brood size or mate attraction. On the contrary, results from the laboratory experiment suggested that male total length and nest size were important during female choice. Females were attracted to and spawned more frequently with larger males holding larger nests. Additionally, females showed a particular preference towards males that displayed intense courtship behaviours. These results suggest that variation in reproductive success among individuals is not random in the common triplefin (F. lapillum) and may be due to a range of complex factors. In natural systems, individual variation in mating success is known to be highly dynamic and vary over time. In Chapter 3, I addressed 3 questions related to reproductive success in male common triplefin: 1) Does the operational sex ratio (OSR) and the density of individuals change predictably within the breeding season? 2) Does male reproductive success change within the breeding season? And 3) Does the age and growth rate of successful males change within the breeding season? To address these questions, I sampled a population of F. lapillum during two periods of the breeding season and quantified a set of morphological and physical traits. Furthermore, I reconstructed individual life histories from the otoliths of egg guarding males. My results show that the density of individuals in the population increased during the summer months, but the operational sex ratio (OSR) remained male-biased. Male reproductive success in terms of brood size and average egg size did not fluctuate during the sampling period. However, the size of males and the size of the nest (cobblestone) held by males was significantly larger in summer compared to winter. Interestingly, successful males sampled in the winter had hatched significantly earlier than successful males sampled in the summer, but their average growth rate remained similar. These findings indicate that variation in male traits across the breeding season plays an important role in female mate choice. The mating system and pool of mating individuals in the common triplefin (F. lapillum) is highly dynamic over the year and has the potential to shape the success of individuals. Overall, this study emphasizes the importance of considering multiple cues and temporal dynamics when disentangling the determinants of individual reproductive success. These findings suggest that male-male competition and female mate choice have a significant influence on male reproductive success. The reproductive ecology of F. lapillum is highly complex and my research has provided valuable insight into its dynamic nature. These results may apply to other species with male parental care and provides an important contribution towards understanding sexual selection and the evolution of mating systems with male parental care.</p>

Disentangling the determinants of reproductive success in a temperate reef fish, Forsterygion lapillum

<p>Identifying sources of individual variation in reproductive success has been a longstanding challenge for evolutionary ecologists. Reproductive success among individuals can be due to several factors such as competition between conspecifics for nest sites and mating partners, mate choice, or by the physical environment. Reproductive success, particularly among males, can be extremely diverse both within and between species and determining which components contribute to success can be particularly challenging. In this thesis, I investigated patterns and drivers of reproductive success in a temperate marine reef fish, Forsterygion lapillum (the common triplefin). Specifically, I examined how male quality, nest quality, and female choice influence male reproductive success. Additionally, I quantified male reproductive success during the winter and summer of the breeding season to examine the temporal dynamics of breeding success in F. lapillum. Selection of mates by females can be driven by the quality and behavioural attributes of the male or by the quality of resources offered. In Chapter 2, using field-based observations, combined with a lab-based study, I evaluated the effects of different male traits and nest characteristics on female choice and male reproductive success. Specifically, I observed egg guarding males in the field during the breeding season and recorded their phenotypic traits, behaviours, and nest characteristics. I then examined their influence on 3 different components of male reproductive success (brood size, individual egg size, and mate attraction). Additionally, I conducted dichotomous choice tests in the laboratory to evaluate female preference for different sized males, holding different sized nests. In the field, I did not detect a significant relationship between male mating success and male total length or nest size. Brood size and individual egg size were highly variable among sampled males, however, further factors such as courtship frequency, and the number of interactions with potential predators did not explain any additional variation. The number of agonistic displays performed by egg guarding males was the only factor to influence egg size, however, it had no direct impact on brood size or mate attraction. On the contrary, results from the laboratory experiment suggested that male total length and nest size were important during female choice. Females were attracted to and spawned more frequently with larger males holding larger nests. Additionally, females showed a particular preference towards males that displayed intense courtship behaviours. These results suggest that variation in reproductive success among individuals is not random in the common triplefin (F. lapillum) and may be due to a range of complex factors. In natural systems, individual variation in mating success is known to be highly dynamic and vary over time. In Chapter 3, I addressed 3 questions related to reproductive success in male common triplefin: 1) Does the operational sex ratio (OSR) and the density of individuals change predictably within the breeding season? 2) Does male reproductive success change within the breeding season? And 3) Does the age and growth rate of successful males change within the breeding season? To address these questions, I sampled a population of F. lapillum during two periods of the breeding season and quantified a set of morphological and physical traits. Furthermore, I reconstructed individual life histories from the otoliths of egg guarding males. My results show that the density of individuals in the population increased during the summer months, but the operational sex ratio (OSR) remained male-biased. Male reproductive success in terms of brood size and average egg size did not fluctuate during the sampling period. However, the size of males and the size of the nest (cobblestone) held by males was significantly larger in summer compared to winter. Interestingly, successful males sampled in the winter had hatched significantly earlier than successful males sampled in the summer, but their average growth rate remained similar. These findings indicate that variation in male traits across the breeding season plays an important role in female mate choice. The mating system and pool of mating individuals in the common triplefin (F. lapillum) is highly dynamic over the year and has the potential to shape the success of individuals. Overall, this study emphasizes the importance of considering multiple cues and temporal dynamics when disentangling the determinants of individual reproductive success. These findings suggest that male-male competition and female mate choice have a significant influence on male reproductive success. The reproductive ecology of F. lapillum is highly complex and my research has provided valuable insight into its dynamic nature. These results may apply to other species with male parental care and provides an important contribution towards understanding sexual selection and the evolution of mating systems with male parental care.</p>

Aposematism facilitates the diversification of parental care strategies in poison frogs

Many organisms have evolved adaptations to increase the odds of survival of their offspring. Parental care has evolved several times in animals including ectotherms. In amphibians, ~ 10% of species exhibit parental care. Among these, poison frogs (Dendrobatidae) are well-known for their extensive care, which includes egg guarding, larval transport, and specialized tadpole provisioning with trophic eggs. At least one third of dendrobatids displaying aposematism by exhibiting warning coloration that informs potential predators about the presence of defensive skin toxins. Aposematism has a central role in poison frog diversification, including diet specialization, and visual and acoustic communication; and it is thought to have impacted their reproductive biology as well. We tested the latter association using multivariate phylogenetic methods at the family level. Our results show complex relationships between aposematism and certain aspects of the reproductive biology in dendrobatids. In particular, aposematic species tend to use more specialized tadpole-deposition sites, such as phytotelmata, and ferry fewer tadpoles than non-aposematic species. We propose that aposematism may have facilitated the diversification of microhabitat use in dendrobatids in the context of reproduction. Furthermore, the use of resource-limited tadpole-deposition environments may have evolved in tandem with an optimal reproductive strategy characterized by few offspring, biparental care, and female provisioning of food in the form of unfertilized eggs. We also found that in phytotelm-breeders, the rate of transition from cryptic to aposematic phenotype is 17 to 19 times higher than vice versa. Therefore, we infer that the aposematism in dendrobatids might serve as an umbrella trait for the evolution and maintenance of their complex offspring-caring activities.

Effects of Group Behavior in The Predatory Raid on Damselfish Nests By The False Cleanerfish Aspidontus Taeniatus

The benefits of group behavior have been reported in a variety of animals. The false cleanerfish Aspidontus taeniatus, which resembles the bluestreak cleaner wrasse Labroides dimidiatus, is the best-known example of mimicry in vertebrates. This mimicry system has been viewed as an aggressive mimicry to bite fish fins. However, recent field studies have reported that large individuals of the false cleanerfish form groups and jointly raid fish nests to eat eggs that are guarded by their parents. Since the cleaner wrasse does not form such groups or specialize in egg-eating, the feeding groups of the false cleanerfish is assumed to reduce the effectiveness of mimicry. Here, we conducted field observations to clarify the functions of group behavior in egg-eating in the false cleanerfish. The false cleanerfish formed groups of 2–12 individuals when they raided breeding nests of 13 damselfish (Pomacentridae) and one triggerfish (Balistidae). The results showed that the group behavior has two effects: a dilution effect, which reduces the risk of being attacked by egg-guarding fish, and an increase in foraging efficiency. We conclude that the false cleanerfish need to form cooperative foraging groups during egg-eating because the egg-guarding parents could see through the mimicry.

Homing and Egg Discrimination in the Western Slimy Salamander,Plethodon albagula(Caudata: Plethodontidae)

In some species of vertebrates egg brooding is a costly form of parental care. Therefore, misdirection of parental care can significantly lower a female’s fitness. Because of the maternal investment and increased survivorship to offspring from egg guarding, a brooding female should home to her nest site after being displaced a short distance and discriminate between her own eggs and eggs from other females. In this study, we experimentally tested, in the field, alternative hypotheses concerning homing ability and egg discrimination in a population of nesting western slimy salamanders (Plethodon albagula). Fourteen brooding females were displaced 1 m to the left or right of their nest sites (determined randomly) for the homing experiment. Furthermore, brooding females (n = 13) were presented with their own clutches, which were displaced 50 cm to the left or right (determined randomly), and unfamiliar egg clutches at their original nest sites. The females were released at an equal distance from both egg clutches. After 24 hours, 12 displaced females (86%) had returned to their own nest sites and were brooding their egg clutches. Also, after 24 hours, nine test females had returned to their own nest sites and were brooding the unfamiliar egg clutches. No control or test females were present at the other new nest site locations. Therefore, we suggest that brooding femaleP. albagulado home to their nest sites and exhibit indirect egg discrimination.

A Neotropical armored harvestman (Arachnida, Opiliones) uses proprioception and vision for homing

Animals use external and/or internal cues to navigate and can show flexibility in cue use if one type of cue is unavailable. We studied the homing ability of the harvestman Heteromitobates discolor (Arachnida, Opiliones) by moving egg-guarding females from their clutches. We tested the importance of vision, proprioception, and olfaction. We predicted that homing would be negatively affected in the absence of these cues, with success being measured by the return of females to their clutches. We restricted proprioception by not allowing females to walk, removed vision by painting the eyes, and removed the odours by removing the clutch and cleaning its surroundings. We found that vision is important for homing, and in the absence of visual cues, proprioception is important. Finally, we found increased homing when eggs were present, and that the time of the day also influenced homing. We highlight vision as a previously overlooked sensory modality in Opiliones.

Hypoxia increases the risk of egg predation in a nest-guarding fish

For fish with parental care, a nest should meet both the oxygenation needs of the eggs and help protect them against predators. While a small nest opening facilitates the latter, it impedes the former and vice versa. We investigated how the presence of potential egg predators in the form of shore crabs Carcinus maenas affects nest building, egg fanning, defensive displays and filial cannibalism of egg-guarding male sand gobies Pomatoschistus minutus under two levels of dissolved oxygen. In the high oxygen treatment, males retained their nest opening size in the presence of crabs, while males in low oxygen built large nest openings both in the absence and presence of crabs, despite the fact that crabs were more likely to successfully intrude into nests with large entrances. Males in low oxygen also fanned more. In the presence of crabs males increased their defensive displays, but while males in high oxygen reduced fanning, males in low oxygen did not. Filial cannibalism was unaffected by treatment. Sand gobies thus prioritize egg ventilation over the protection afforded by small nest openings under hypoxia and adopt defensive behaviour to avert predator attention, even though this does not fully offset the threat from the egg predators.

Egg-guarding behavior of the treehopper Ennya chrysura (Hemiptera: Membracidae): female aggregations, egg parasitism, and a possible substrate-borne alarm signal

Treehoppers are known for their substrate-borne communication and some of them also for their subsocial behavior. Following a more general study of the natural history and substrate-borne signal repertoire of the treehopper Ennya chrysura, the objective of this paper was to explore in greater depth the signals and other behaviors associated specifically to egg-guarding. Theese were studied both in natural and laboratory conditions between July, 2000 and March, 2004. The spacial distribution of egg guarding females was studied in the natural population; recording equipment and playback experiments were used in the laboratory and then analyzed digitally. Under natural conditions (San Antonio de Escazú, Costa Rica), female E. chrysura guard their egg masses and egg-guarding was associated with lower parasitism of the eggs from the wasps Gonatocerus anomocerus and Schizophragma sp. (Mymaridae). Females tended to place their eggs close to other egg-guarding females and they produced substrate-borne vibrations when disturbed. An aggregated pattern under natural conditions was confirmed by calculating dispersion indices from egg-clutch data obtained from 66 leaves in the field. The disturbance signal was characterized from laboratory recordings of substrate-borne vibrations of 10 egg-guarding females. Experiments conducted in the laboratory with 18 egg-guarding females showed that those which were previously exposed to the disturbance signal of another female moved slightly or vibrated more during playbacks and that they reacted more quickly and exhibited more deffensive behaviors in response to a tactile stimulus. The signals produced while defending against egg parasites may therefore function as an alarm and favor aggregating behavior of egg-guarding females.

Foraging, oviposition sites and notes on the natural history of the harvestman Heteromitobates discolor (Opiliones, Gonyleptidae)

The lack of data on the natural history often hampers phylogenetic studies on the evolution of behavior. Herein we provide quantitative field data on foraging and oviposition sites of a Neotropical harvestman belonging to a subfamily with a published phylogeny, Goniosomatinae. Heteromitobates discolor rests during the day on granitic boulders on rivers, laying eggs in sheltered and darker areas. The female guard the eggs and aggressively respond to approaching conspecific females. In the absence of the female, ants, conspecifics and reduviids may predate the eggs. Egg-guarding females are known not to leave the clutch, but males and non-guarding females may leave the granitic boulders and forage on the vegetation at night, close to the river margins and with no difference in the sites explored between males and females. The general features described in H. discolor are similar to what has been reported for other species in this subfamily, suggesting an evolutionary conservatism within the group.