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ABSTRACT: Circulating corticosteroids have been related to social status in a variety of species. However, our understanding of corticosteroid receptor expression and its relationship with sociality is still in its infancy. Knowledge of variation in receptor expression is critical to understand the physiological relevance of differences in circulating corticosteroid concentrations. In this study, we examined corticosteroid receptor gene expression in relation to dominance rank, sex, and social behaviour in the highly social cichlid fish, Neolamprologus pulcher. We examined the relative gene expression of the three known teleost corticosteroid receptors: glucocorticoid receptor 1 (GR1), glucocorticoid receptor 2 (GR2), and the mineralocorticoid receptor (MR) in liver and brain tissue of dominant and subordinate N. pulcher males and females. Phylogenetic analysis revealed the N. pulcher gene originally described as GR2, clustered with other teleost GR1 genes, while the originally-described N. pulcher GR1 gene clustered with the GR2 genes of other teleosts. Therefore we propose a change in the original nomenclature of the N. pulcher GRs: GR1 (formerly GR2) and GR2 (formerly GR1) and adopt this new nomenclature throughout this manuscript. Liver MR transcript levels were higher in males than females, and positively related to submissive behaviour. Liver GR2 (formerly GR1) transcript levels were also higher in males than females. Collectively, the results demonstrate sex differences in corticosteroid receptor abundance, and suggest tissue- and receptor-specific roles for corticosteroid receptors in mediating aspects of social behaviour.
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 12/2012; · 2.20 Impact Factor
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ABSTRACT: Many animals fight to win resources, repel competitors or establish dominance in a social group. Mutual-assessment of fighting ability, where competitors gather and compare information about their opponent's as well as their own fighting ability has been the dominant theoretical framework for understanding decision-making during fights. However, self-assessment, where each individual has a cost threshold and fights up until that point, may be more common than previously appreciated. In this study, we attempted to discriminate between these two potential assessment mechanisms in a group-living cichlid fish, Neolamprologus pulcher by probing aggressive motivation during a territorial contest. We measured aggressive motivation, and used this metric to investigate assessment rules during an ongoing contest. We predicted that if these social fish use self-assessment, we would observe a positive correlation between the fighting ability of the probed animal and its aggressive motivation. Alternatively, if mutual-assessment is used then we predicted we would find a negative effect of the opponent's fighting ability on the aggressive motivation of the probed fish because fish should be less motivated to fight against formidable opponents. Our results did not support either of these predictions. In contrast we found that small individuals were more aggressively motivated regardless of their opponent's size. We discuss this result in the context of theoretical models of aggression in individuals of small body size.
Behavioural processes 10/2012; · 1.53 Impact Factor
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ABSTRACT: Oxytocin and its nonmammalian homologues play an important role in modulating a diverse array of social behaviours. Recently, it has been suggested that one of the key functions of oxytocin is to direct attention towards socially relevant stimuli, increase social motivation and guide social decision making. Here, we test whether an exogenous increase in isotocin (the teleost homologue of oxytocin) increases the response to social information in a cooperative breeder, the highly social cichlid fish, Neolamprologus pulcher. In our first experiment (a simulated territorial contest), we found that N. pulcher injected with isotocin were more sensitive to the size of their opponent regardless of whether their opponent was a live rival or a mirror image. Isotocin-treated fish fought in accordance with the size of their opponent whereas control fish fought according to their intrinsic aggressive propensity. In our second experiment (a social group context), we found that isotocin-treated N. pulcher were more responsive to aggressive feedback and produced more submissive displays (an important social signal in this species). These experiments provide evidence that isotocin increases responsiveness to social information and further support the function of the oxytocin family of nonapeptides as a highly conserved regulator of social behaviour across vertebrates. The evolution of sociality represents one of the most enduring and important questions in behavioural biology (Székely et al. 2010). Why do some species show complex social behaviour, while other closely related species living in similar ecologies spend the majority of their lives in solitude? To answer this question, it is crucial that we develop an integrative perspective on social behaviour that includes a thorough understanding of the proximate mechanisms that generate social behaviour (Insel & Fernald 2004; Young 2009; Soares et al. 2010). The nonapeptide oxytocin (and its nonmammalian homologues; e.g. isotocin in teleost fish, mesotocin in birds and reptiles) represents a promising candidate system for the modulation of social behaviour (for recent reviews see: Donaldson & Young 2008; Goodson 2008; Lee et al. 2009; Ross & Young 2009; Goodson & Thompson 2010; Insel 2010). Oxytocin acts both as a central neuromodulator and a peripheral hormone (Lee et al. 2009). In the periphery, oxytocin is involved in parturition and milk letdown (Lee et al. 2009). Centrally, oxytocin is essential for the regulation of behaviours related to reproduction, including pair bonding and parental care (Insel & Young 2001). A growing body of research has linked variation in oxytocin and its receptor to social behaviours outside of the realm of reproduction, including affiliation, attachment, trust, generosity, the formation of social memories and the suppression of social anxiety (MacDonald & MacDonald 2010). Taken together, this research suggests that the oxytocin system may be a very general mechanism involved in the regulation of social behaviour (Ross & Young 2009; Goodson & Thompson 2010). The oxytocin system is highly pleiotropic, affecting an impres-sive diversity of behaviours across functional contexts (e.g. parental care, cooperation, aggregation, anxiety and aggression). One possible explanation for this functional diversity is that oxytocin may be centrally involved in a higher-order regulatory system with downstream effects on a wide variety of social behaviours tran-scending functional context (Ross & Young 2009; O'Connell & Hofmann 2011). Recently, a unifying principle has been proposed for the function of oxytocin as a central modulator of attention to social stimuli (Ross & Young 2009). Individuals or species with greater expression of oxytocin (higher circulating levels and/or greater receptor density) may be more attentive to socially relevant stimuli and as a result may be more socially motivated. In support of this idea, it seems that the effects of oxytocin manipulations are specific to explicitly social contexts, while other functionally similar but nonsocial behaviours remain unaffected (Nelson & Panksepp 1996; Ferguson et al. 2000; MacDonald & MacDonald 2010). For example, Kosfeld et al. (2005) found that humans treated with exogenous oxytocin were more accepting of risk in a socially framed economic game (which the authors interpreted as
Animal Behaviour 08/2012; 84:753-760. · 3.49 Impact Factor
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ABSTRACT: Activity levels are modulated by trade-offs between reducing predation risk and the need to move in order to find food or
mates. Because these trade-offs affect males and females differently, many species show sex-specific movement, dispersal patterns,
and spatial navigation capacities, with the sex that gains the most from territory ownership often dispersing less. Unlike
mammals and birds, sex differences in movement among fishes remain poorly studied, and the connections between tests of movement
propensity in the laboratory and in the field are rarely made. Here, we examine the differences in movement between male and
female round goby (Neogobius melanostomus) in both laboratory and field settings. This fish species is invasive in North America and currently undergoing further range
expansions. In the laboratory, round goby males were more active and explored a novel environment more readily than did females.
A large-scale mark–recapture study in Lake Ontario over twoyears revealed that males moved more than females between years,
but there were no within-year sex differences. Thus, round goby display male-biased movement patterns, providing a comparison
point to dispersal patterns in other taxa. Understanding sex-specific movement of round goby in the field will also help predict
dispersal and population dynamics, both in areas where round goby have already become established and where they are continuing
to invade.
KeywordsHome range–Dispersal–Boldness–Activity–Exploration–Invasive species–Sex differences–Mark–recapture–
Neogobius melanostomus
Behavioral Ecology and Sociobiology 05/2012; 65(12):2239-2249. · 3.18 Impact Factor
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ABSTRACT: Among taxonomically widespread cooperatively breeding vertebrates, those with non-breeding helpers-at-the-nest provide an
excellent opportunity to understand the proximate mechanisms underlying care and allocare. In this study, we examined androgen
levels in relation to care behavior in a cooperatively breeding cichlid fish, Neolamprologus pulcher, from Lake Tanganyika. We concentrated on androgens, as these hormones have been linked to the defense behavior, and the
defense of young is a common form of parental care in fishes. N. pulcher dominant female breeders performed the most care and also displayed the highest levels of plasma testosterone (T) compared
with other individuals within the social group. We also found that dominant male breeders provided a similar amount of care
as did the subordinate helpers, but breeding males had the highest levels of 11-ketotestosterone (11KT), an important androgen
in fish. Breeders had higher levels of both androgens (T and 11KT) compared to helpers. There was a weak but significant positive correlation between T levels and the frequency of
care regardless of sex and status. Our results suggest that androgens may promote defense of young and are in contrast to
the commonly reported trade-off between androgen and parental care.
Behavioral Ecology and Sociobiology 04/2012; 62(5):785-794. · 3.18 Impact Factor
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ABSTRACT: Most introduced non-native species fail to establish as a result of mortality or reproductive failure. An established population
can increase the probability of survival and reproductive success of newly introduced individuals by reducing both Allee effects
and demographic stochasticity. Previously, attention has been paid to the establishment phase of the invasion process and
its probability modelled as a stochastic process, while the spread phase has received less attention. By analyzing data collected
during the spread phase of an invasion of the round goby, Neogobius melanostomus, in Hamilton Harbour, Lake Ontario, we develop an analytical approach to backcalculate the time to establishment and to determine
the time to habitat saturation. Our modelling shows that: (1) during the transition between arrival and establishment, propagule
pressure in the form of new adults entering the area can be very low and still represent a significant probability of establishment;
(2) much higher concentrations of juveniles would be needed to pose a significant risk of invasion; (3) the demographic contribution
of propagule pressure during the spread phase is low and its total elimination will not halt population growth and spread;
(4) a short elapsed time between arrival and establishment indicated that the transition between these two phases can be characterized
as a deterministic process with high propagule pressure and low adult mortality rates; and, (5) very aggressive management
actions would be needed to halt population growth after population establishment, suggesting that preventative measures are
the most effective management options available to reduce risk of future invasions.
KeywordsGobidae-Great Lakes-Propagule pressure-Habitat saturation-Establishment probability-Invasive species
Biological Invasions 04/2012; 12(11):3861-3875. · 2.90 Impact Factor
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ABSTRACT: There is increasing concern for the disruptive effects seen in aquatic species exposed to environmental contaminants. However,
few studies have investigated the impact of such contaminants on the behavior of individuals living in exposed waters. Contaminant
exposure can affect animal populations by disrupting behaviors including feeding, locomotion, and mating. In this study, we
examined how living in an ecosystem polluted by combinations of polycyclic aromatic hydrocarbons, polychlorinated biphenyls,
and heavy metals (arsenic, cadmium, iron, lead, zinc) impacts contest behavior in the round goby (Neogobius melanostomus). Fish collected from heavily contaminated and cleaner sites in Lake Ontario were subjected to a resource contest to determine
the effect of these contaminants on aggression and the establishment of dominance hierarchies, which in turn influence access
to food, shelter, and mating opportunities. Dominance establishment (a clear resource winner) was less obvious among fish
from the contaminated site compared to the more stable hierarchies that formed between pairs of fish from the clean site.
Pairs of fish from the contaminated site performed more assessment displays compared to fish from clean sites. These results
suggest that the costs of living in an environment under exposure can shape behavioral repertoires. The altered conflict resolution
strategies of contaminated fish may reflect impaired cognitive function, sensory perception, and/or higher metabolic load
associated with aggression. This study provides support for the utilization of quantifiable behavioral differences as ecologically
relevant measures of contaminant exposure.
KeywordsRound goby-Intra-specific competition-Aggression-Contest structure-Aquatic pollutants-
Neogobius melanostomus
Behavioral Ecology and Sociobiology 04/2012; 64(12):1947-1958. · 3.18 Impact Factor
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ABSTRACT: Changes in animal movement (frequency or speed of locomotion) following exposure to a toxicant are frequently considered a biomarker of contaminant exposure and are some of the most widely reported behavioral results in toxicological literature. However, the ecological consequences of such behavioral changes, such as effects on toxicant transfer in foodwebs, are far less well understood, complicated in part by the short-term nature of laboratory experiments and the lack of complementary field studies where the nature of toxicant exposure is more complex. Here we examine whether naturally exposed individuals of the round goby, a benthic, site-loyal fish, move in a manner similar to conspecifics from less contaminated habitats. In the laboratory, round goby from a relatively cleaner site showed greater activity and exploration than goby from two highly contaminated sites. Male fish were more active than females but the site effects were similar in both sexes. In contrast to laboratory findings, a field mark-recapture study of 881 round goby showed that fish from the cleaner site did not move greater distances or exhibit shorter residence times within the site than round goby from highly contaminated sites. Our results indicate that while behavioral changes in the laboratory may be one of several useful diagnostics of toxicant exposure of wild-exposed animals, they do not necessarily translate readily into measurable differences in a natural context. Thus, the potential fitness consequences of toxicant exposure based on behavioral changes need to be assessed carefully.
Ecotoxicology 01/2012; 21(4):1003-12. · 2.36 Impact Factor
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ABSTRACT: The conundrum of why subordinate individuals assist dominants at the expense of their own direct reproduction has received much theoretical and empirical attention over the last 50 years. During this time, birds and mammals have taken centre stage as model vertebrate systems for exploring why helpers help. However, fish have great potential for enhancing our understanding of the generality and adaptiveness of helping behaviour because of the ease with which they can be experimentally manipulated under controlled laboratory and field conditions. In particular, the freshwater African cichlid, Neolamprologus pulcher, has emerged as a promising model species for investigating the evolution of cooperative breeding, with 64 papers published on this species over the past 27 years. Here we clarify current knowledge pertaining to the costs and benefits of helping in N. pulcher by critically assessing the existing empirical evidence. We then provide a comprehensive examination of the evidence pertaining to four key hypotheses for why helpers might help: (1) kin selection; (2) pay-to-stay; (3) signals of prestige; and (4) group augmentation. For each hypothesis, we outline the underlying theory, address the appropriateness of N. pulcher as a model species and describe the key predictions and associated empirical tests. For N. pulcher, we demonstrate that the kin selection and group augmentation hypotheses have received partial support. One of the key predictions of the pay-to-stay hypothesis has failed to receive any support despite numerous laboratory and field studies; thus as it stands, the evidence for this hypothesis is weak. There have been no empirical investigations addressing the key predictions of the signals of prestige hypothesis. By outlining the key predictions of the various hypotheses, and highlighting how many of these remain to be tested explicitly, our review can be regarded as a roadmap in which potential paths for future empirical research into the evolution of cooperative breeding are proposed. Overall, we clarify what is currently known about cooperative breeding in N. pulcher, address discrepancies among studies, caution against incorrect inferences that have been drawn over the years and suggest promising avenues for future research in fishes and other taxonomic groups.
Biological Reviews 05/2011; 86(2):511-30. · 9.07 Impact Factor
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Patrick Abbot,
Jun Abe,
John Alcock,
Samuel Alizon,
Joao A C Alpedrinha,
Malte Andersson,
Jean-Baptiste Andre,
Minus van Baalen,
Francois Balloux, Sigal Balshine, [......],
Stuart A West,
Mary Jane West-Eberhard,
David F Westneat,
Diane C Wiernasz,
Geoff Wild,
Richard Wrangham,
Andrew J Young,
David W Zeh,
Jeanne A Zeh,
Andrew Zink
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ABSTRACT: Arising from M. A. Nowak, C. E. Tarnita & E. O. Wilson 466, 1057-1062 (2010); Nowak et al. reply. Nowak et al. argue that inclusive fitness theory has been of little value in explaining the natural world, and that it has led to negligible progress in explaining the evolution of eusociality. However, we believe that their arguments are based upon a misunderstanding of evolutionary theory and a misrepresentation of the empirical literature. We will focus our comments on three general issues.
Nature 03/2011; 471(7339):E1-4; author reply E9-10. · 36.28 Impact Factor
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ABSTRACT: Elevated stress experienced by a mother can compromise both her own reproductive success and that of her offspring. In this study, we investigated whether chronically stressed mothers experienced such effects in cooperatively breeding species, in which helpers at the nest potentially compound the negative effects of maternal stress. Using Neolamprologus pulcher, a group-living cichlid fish from Lake Tanganyika, we observed the effects of experimentally increased stress on female reproductive success (measured as inter-spawn interval, and number of eggs) as well as egg characteristics including egg size and cortisol concentrations. Stress levels were manipulated by repeated exposure to the acute stresses of chasing and netting. Stressed females had longer inter-spawn intervals and laid fewer, smaller eggs. Although no significant differences in egg cortisol concentrations were detected between control and stressed females, egg cortisol concentration fell between spawns in control but not in stressed fish. No effect of helper number was detected for any parameter examined, except there appeared to be less change in egg cortisol content in groups with helpers present. Our results suggest that stress imposes fitness costs on breeding females, and social regulation of a dominance hierarchy does not appear to exacerbate or alleviate the negative effects of maternal stress.
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 01/2011; 158(1):22-9. · 2.20 Impact Factor
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ABSTRACT: The invasive round goby has a recognised role in transferring contaminants through foodwebs, but little work has been done on contaminant impacts on round gobies themselves. Here we present the first case study of contaminant biomarkers and subpopulation structure variation in round gobies, in relation to habitat contamination, within a Canadian Area of Concern, Hamilton Harbour. Copper and cadmium were elevated in livers of fish from contaminated habitats. Although catch abundances were similar across sites, fish were smaller, a greater proportion of fish were female and more males were in reproductive condition in contaminated sites. Fish from contaminated areas showed more fin loss. Males from contaminated sites showed intersex gonads and genitalia. Ethoxyresorufin-o-deethylase (EROD) activity was higher in fish collected near polycyclic aromatic hydrocarbon (PAH)-rich sediments. The results indicate that contaminants impact the characteristics of round goby populations, which could affect ecosystems beyond toxicant biomagnification. This study also confirms that round gobies can be abundant in polluted habitats, which may draw predators-facilitating mobilisation of contaminants in foodwebs.
Ecotoxicology and Environmental Safety 10/2010; 73(7):1755-64. · 2.29 Impact Factor
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ABSTRACT: Cerebral lateralization, an evolutionarily ancient and widespread phenomenon among vertebrates, is thought to bestow cognitive advantages. The advantages of lateralization at the individual-level do not necessarily require that the entire population share the same pattern of lateralization. In fact, directional bias in lateralization may lead to behavioural predictability and enhanced predator success or prey evasion. Recent theory has suggested that population-level lateralization may be favored if individuals are better able to perform coordinated behaviours, providing a distinct advantage in cooperative contexts. Here we test whether the highly social, cooperatively breeding cichlid fish Neolamprologus pulcher shows lateralized responses to a social stimulus. We found population-level biases in males; on average male N. pulcher use their right eye/left hemisphere to view their mirror image. Individual females had a preferred hemisphere, but these preferences appeared not to be directionally aligned among females. We discuss these results in the context of coordinated social behaviour and suggest future research directions.
Behavioural processes 09/2010; 85(1):68-71. · 1.53 Impact Factor
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ABSTRACT: Social aggression is one of the most conspicuous features of animal societies, yet little is known about the causes of individual variation in aggression within social hierarchies. Recent theory suggests that when individuals form queues for breeding, variation in social aggression by non-breeding group members is related to their probability of inheriting breeding status. However, levels of aggression could also vary as a temporary response to changes in the hierarchy, with individuals becoming more aggressive as they ascend in rank, in order to re-establish dominance relationships. Using the group-living fish, Neolamprologus pulcher, we show that subordinates became more aggressive after they ascended in rank. Female ascenders exhibited more rapid increases in aggression than males, and the increased aggression was primarily directed towards group members of adjacent rather than non-adjacent rank, suggesting that social aggression was related to conflict over rank. Elevated aggression by ascenders was not sustained over time, there was no relationship between rank and aggression in stable groups, and aggression given by ascenders was not sex-biased. Together, these results suggest that the need to re-establish dominance relationships following rank ascension is an important determinant of variation in aggression in animal societies.
Biology letters 09/2010; 7(2):190-3. · 3.76 Impact Factor
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ABSTRACT: A growing concern over endocrine disruption in aquatic species has prompted the development of molecular assays to monitor environmental impacts. This study describes the development of quantitative polymerase chain reaction (qPCR) assays to characterize the expression of two vitellogenin (Vtg) genes in the invasive round goby (Neogobius melanostomus). Fragments from the 18SrRNA (housekeeping gene), Vtg II, and Vtg III genes were cloned and sequenced. The qPCR assays were developed to detect hepatic Vtg expression in goby. The assays detected induction of both Vtg genes in nonreproductive males following a two-week laboratory exposure to 17β-estradiol (≥1 mg/kg i.p. injection). The assays were applied to goby from Hamilton Harbour, Lake Ontario (Canada), including those from sites where feminization and intersex of goby has been documented. Both Vtg genes had significantly higher expression in females compared to males. Male reproductive goby adopt either parental or sneaker tactics; Vtg II expression was higher in sneaker than in parental males but parental and nonreproductive males did not differ from each other. The Vtg III expression was significantly higher in sneaker males followed by parental males and nonreproductive males, respectively. The Vtg II and III expression in nonreproductive males was elevated in the contaminated site with documented intersex. This assay provides an important tool for the use of an invasive species in monitoring endocrine disruption in the Great Lakes region.
Environmental Toxicology and Chemistry 08/2010; 29(12):2751-60. · 2.81 Impact Factor
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Hereditas 10/2009; 146(5):204-7. · 0.79 Impact Factor
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ABSTRACT: Alternative male reproductive tactics are taxonomically widespread. In such species, parental, or conventional, males express secondary sexual characteristics, court females and guard offspring, while smaller parasitic or sneaker males avoid the costs of courtship and parental care by performing sneak fertilizations. Theory predicts that sneakers will invest more in testes mass and produce more competitive ejaculates than parentals because sneakers always experience sperm competition while parental males experience sperm competition only when a sneaker is present. Here we present convergent lines of evidence supporting the existence of alternative male reproductive tactics in round gobies (Apollonia melanostoma, formerly Neogobius melanostomus), a recent invader in the Great Lakes. Dark morph males exhibited secondary sexual characteristics, were larger and had higher plasma 11-ketotestosterone concentrations than light morphs, while light morph males invested more in ejaculates (both testes mass and sperm density). Both male morphs had enlarged urogenital papillae, but papillae were relatively longer in light morph males. Sperm tail length did not differ between morphs, and sperm from dark morphs swam faster than sperm from light morphs. Our data strongly argue for the presence of alternative tactics in round gobies, support some predictions from sperm competition theory and align with empirical observations in other taxa. For species of concern like the invasive round goby, it is critical to consider such evidence of alternative male mating tactics when constructing population growth models and assessment of invasion success and impacts.
Journal of Great Lakes Research 06/2009; · 1.52 Impact Factor
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ABSTRACT: Sperm competition, the contest among ejaculates from rival males to fertilize ova of a female, is a common and powerful evolutionary force influencing ejaculate traits. During competitive interactions between ejaculates, longer and faster spermatozoa are expected to have an edge; however, to date, there has been mixed support for this key prediction from sperm competition theory. Here, we use the spectacular radiation of cichlid fishes from Lake Tanganyika to examine sperm characteristics in 29 closely related species. We provide phylogenetically robust evidence that species experiencing greater levels of sperm competition have faster-swimming sperm. We also show that sperm competition selects for increases in the number, size, and longevity of spermatozoa in the ejaculate of a male, and, contrary to expectations from theory, we find no evidence of trade-offs among sperm traits in an interspecific analysis. Also, sperm swimming speed is positively correlated with sperm length among, but not within, species. These different responses to sperm competition at intra- and interspecific levels provide a simple, powerful explanation for equivocal results from previous studies. Using phylogenetic analyses, we also reconstructed the probable evolutionary route of trait evolution in this taxon, and show that, in response to increases in the magnitude of sperm competition, the evolution of sperm traits in this clade began with the evolution of faster (thus, more competitive) sperm.
Proceedings of the National Academy of Sciences 02/2009; 106(4):1128-32. · 9.68 Impact Factor
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ABSTRACT: Hypoxia (low oxygen) exposure generally leads to decreased reproductive capacity, exhibited by reductions in testicular mass, reproductive hormones, and sperm swimming speed. However, in many fish species, reproduction occurs either periodically or exclusively under hypoxic conditions. In this study we assessed how hypoxia influences sperm per-formance in the plainfin midshipman (Porichthys notatus Girard, 1854), a species that lives in intertidal nests that become hypoxic during low tides. We exposed sperm from the same male to normoxic or hypoxic conditions and compared sperm characteristics and oxygen consumption between treatments. Sperm exposed to hypoxic water swam faster and consumed more oxygen than sperm swimming in normoxic conditions. Sperm swimming speed was positively related with oxygen consumption. For each male, the percentage of motile spermatozoa did not differ between treatments, suggesting that the same number of sperm were active but their performance was dependent on the dissolved oxygen content in the water. We discuss the implications of our results in the context of sperm competition and fertilization success under hypoxic con-ditions. Résumé : Une exposition à l'hypoxie (faibles concentrations d'oxygène) mène généralement à une diminution de la ca-pacité reproductive, ce qui se manifeste par une réduction de la masse testiculaire, des hormones reproductives et de la vi-tesse de nage des spermatozodes. Cependant, chez plusieurs espèces de poissons, la reproduction a lieu périodiquement ou même exclusivement dans des conditions d'hypoxie. Dans notre étude, nous évaluons les influences de l'hypoxie sur la performance des spermatozodes chez le pilotin tacheté (Porichthys notatus Girard, 1854), une espèce qui vit dans des nids intertidaux qui deviennent hypoxiques à marée basse. Nous avons exposé les spermatozodes d'un même mâle à des condi-tions normoxiques ou hypoxiques et avons comparé les caractéristiques des spermatozodes et leur consommation d'oxygène dans les deux conditions expérimentales. Les spermatozodes exposés à l'eau hypoxique nagent plus rapidement et consomment plus d'oxygène que les spermatozodes qui nagent en conditions normoxiques. Il y a une relation positive entre la vitesse de nage des spermatozodes et leur consommation d'oxygène. Chez un même mâle, le pourcentage de sper-matozodes mobiles ne varie pas d'un traitement à l'autre, ce qui laisse croire qu'il y a le même nombre de spermato-zodes en activité, mais que leur performance dépend de la concentration d'oxygène dissous dans l'eau. Nous discutons des implications de nos résultats dans le cadre de la compétition spermatique et du succès de la fécondation dans des con-ditions hypoxiques. [Traduit par la Rédaction]
Canadian Journal of Zoology 01/2009; · 1.21 Impact Factor
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ABSTRACT: The evolution of cooperative behaviour, whereby individuals enhance the fitness of others at an apparent cost to themselves, represents one of the greatest paradoxes of evolution. Individuals that engage in such cooperative behaviour can, however, be favoured by natural selection if cooperative actions confer higher fitness than alternative actions. To understand the evolution of cooperative behaviour, the direct and indirect genetic benefits that individuals accrue in the present and future must be summed - this can be accomplished without any reference to the colorful vocabulary typically associated with studies of cooperation. When benefits are accrued indirectly through relatives or directly in the future individuals must be able to assess and enhance their probability of accruing those benefits and behave accordingly. We suggest that, in the same way that studies of kin recognition systems improved our understanding of how individuals assess and enhance their probability of accruing indirect benefits, studies of various forms of inheritance and reciprocation recognition systems will improve our understanding of how individuals assess and enhance their probability of accruing future benefits. Recognizing the parallel between studies of indirect fitness and future fitness, at multiple levels of analysis, will move us toward a simpler and more consistent framework for understanding the evolution of cooperative behaviour.
Behavioural Processes 11/2007; 76(2):152-9. · 1.65 Impact Factor
