The influence of eutrophication on sexual selection in sticklebacks

Jordens ekologiska system undergår för tillfället stora förändringar pga. människans aktiviteter. Ett växande antal studier visar att dessa förändringar påverkar naturliga och sexuella urvalet och därmed evolutiva processer. Målet med detta arbete var att undersöka effekterna av omgivningsförändringar på sexuella urvalet genom att använda den ökade övergödningen inom storpiggen Gasterosteus aculeatus lekområden som modell system. Sexuella urvalet är en viktig evolutiv kraft med följder på populations- och artnivå (Kapitel 1). Avhandlingens olika delar fokuserar på övergödningens effekter på upptäckandet av partners, användningen av visuella- och doftsignaler i partnersval, och fördelningen av parningsframgången mellan bobyggande hanar. I Kapitel II och III simuleras hur grumlighet orsakad av fytoplankton påverkar hastigheten med vilken potentiella partners påträffas, genom effekter på synligheten. Resultaten visar att normala algblomningar i Östersjön har en måttlig effekt på finnandet av potentiella partners. Detta tyder på att algblomningarna troligen inte kommer att minska på selektiva parningen pga. ökade sökkostnader. I Kapitel IV visas att storspiggen ändrar relativa användningen av olika signaler när vattnets grumlighet ökar; visuella signaler minskar i betydelse medan doftsignaler ökar i betydelse. Samtidigt underlättas användandet av doftsignaler av ändringar i vattnets kemiska sammansättning då fotosyntesen intensifieras (Kapitel V). Lek i övergödda vatten kan ändå vara kostsamt både på individ- och populationsnivån, då parasiterade hanar, som troligen är dåligt genetiskt anpassade till sin miljö, lyckas få mer ägg i sina bon än friskare hanar som troligen är av högre genetisk kvalitet (Kapitel VI). Övergödningen påverkar således partnersval och konkurrensen om partners genom att påverka upptäckandet av potentiella partners, evalueringen av partners och fördelningen av partners inom lekområdena. De följder detta kan ha för evolutionen av sexuellt selekterad egenskaper och för populationers dynamik och livskraft är dock oklara. Avhandlingen visar på svårigheten att förutse följderna av omgivningsförändringar för sexuella urvalet och effekterna på individ och populationsnivå.

Behavioural responses to anthropogenic disturbances

When a habitat undergoes change, the first response of an individual is often behavioural adjustment. This immediate response can determine whether the population will survive or not, as behavioural flexibility gives time for genetic changes to arise later on. Habitat changes that alter reproductive behaviours can have long-lasting effects on populations. If the selective regime has changed under the new conditions, mate choice cues may no longer reliably reflect an individual s quality. Thus, animals have to be able to adjust their reproductive behaviours to the local conditions. The aim of my thesis was to discuss if and how animals are able to respond to rapid anthropogenic environmental change, and to study the mechanisms of the responses and the evolutionary consequences. The main focus was on the effects of human-induced eutrophication on the reproductive behaviour of fishes. Eutrophication is the result of increased nutrient input and can cause dense underwater vegetation and algal blooms. I used fishes from two very different ecosystems as model species, the Baltic Sea threespine stickleback (Gasterosteus aculeatus) and the desert goby (Chlamydogobius eremius), an endemic species of the Lake Eyre region in Central Australia. I investigated the effects of increased habitat complexity on courtship behaviour and the possibility of local differentiation in courtship and nest building behaviour depending on the level eutrophication in the habitat of origin. Furthermore, I observed the effect of turbidity on stickleback nest building behaviour. The results show that threespine stickleback males, which were born in areas that have been eutrophied for decades, court females at a higher intensity than males from clear water areas. Similarly, male desert gobies increased their courtship effort in dense vegetation. Intense courtship could be an adjustment to reduced visibility and lowered predation risk in the densely vegetated sites. However, there were no clear differences in nest building between males from clear and eutrophied areas under standardized conditions. This was expected as Baltic Sea sticklebacks prefer to nest under vegetation cover and are fairly rigid in adjusting their nest characteristics. Nest building was affected by increased turbidity: males built smaller nests with a larger nest entrance in turbid water. The large variation in the magnitude of phytoplankton blooms may require a rapid adjustment of the optimal nest structure to the current conditions. This thesis highlights the complex interactions that are set- off by human-induced changes in habitats and are followed by the immediate behavioural responses. It also encourages more research to tease apart the phenotypic and genetic components of the observed behavioural differences.

Matching sender and receiver: poikilothermy and frequency tuning in a tree cricket

Animals communicate in non-ideal and noisy conditions. The primary method they use to improve communication efficiency is sender-receiver matching: the receiver's sensory mechanism filters the impinging signal based on the expected signal. In the context of acoustic communication in crickets, such a match is made in the frequency domain. The males broadcast a mate attraction signal, the calling song, in a narrow frequency band centred on the carrier frequency (CF), and the females are most sensitive to sound close to this frequency. In tree crickets, however, the CF changes with temperature. The mechanisms used by female tree crickets to accommodate this change in CF were investigated at the behavioural and biomechanical level. At the behavioural level, female tree crickets were broadly tuned and responded equally to CFs produced within the naturally occurring range of temperatures (18 to 27 degrees C). To allow such a broad response, however, the transduction mechanisms that convert sound into mechanical and then neural signals must also have a broad response. The tympana of the female tree crickets exhibited a frequency response that was even broader than suggested by the behaviour. Their tympana vibrate with equal amplitude to frequencies spanning nearly an order of magnitude. Such a flat frequency response is unusual in biological systems and cannot be modelled as a simple mechanical system. This feature of the tree cricket auditory system not only has interesting implications for mate choice and species isolation but may also prove exciting for bio-mimetic applications such as the design of miniature low frequency microphones.

Changing resonator geometry to boost sound power decouples size and song frequency in a small insect

Despite their small size, some insects, such as crickets, can produce high amplitude mating songs by rubbing their wings together. By exploiting structural resonance for sound radiation, crickets broadcast species-specific songs at a sharply tuned frequency. Such songs enhance the range of signal transmission, contain information about the signaler's quality, and allow mate choice. The production of pure tones requires elaborate structural mechanisms that control and sustain resonance at the species-specific frequency. Tree crickets differ sharply from this scheme. Although they use a resonant system to produce sound, tree crickets can produce high amplitude songs at different frequencies, varying by as much as an octave. Based on an investigation of the driving mechanism and the resonant system, using laser Doppler vibrometry and finite element modeling, we show that it is the distinctive geometry of the crickets' forewings (the resonant system) that is responsible for their capacity to vary frequency. The long, enlarged wings enable the production of high amplitude songs; however, as a mechanical consequence of the high aspect ratio, the resonant structures have multiple resonant modes that are similar in frequency. The drive produced by the singing apparatus cannot, therefore, be locked to a single frequency, and different resonant modes can easily be engaged, allowing individual males to vary the carrier frequency of their songs. Such flexibility in sound production, decoupling body size and song frequency, has important implications for conventional views of mate choice, and offers inspiration for the design of miniature, multifrequency, resonant acoustic radiators.

The role of tusks, musth and body size in male-male competition among Asian elephants, Elephas maximus

The evolution of sexually dimorphic, elaborate male traits that are seemingly maladaptive may be driven by sexual selection (male-male competition and or female mate choice). Tusk possession in the Asian elephant is sexually dimorphic and exaggerated but its role in male-male competition has not yet been determined. We examined the role of the tusks in establishing dominance along with two other known male-male signals, namely, body size and musth (a temporary physiologically heightened sexual state) in an Asian elephant population in northeastern India with equal proportions of tusked and tuskless males. We observed 116 agonistic interactions with clear dominance outcomes between adult (>15 years) males during 458 field days in the dry season months of 2008-2011. A generalized linear mixed-effects model was used to predict the probability of winning as a function of body size, tusk possession and musth status relative to the opponent. A hierarchy of the three male-male signals emerged from this analysis, with musth overriding body size and body size overriding tusk possession. In this elephant population tusk possession thus plays a relatively minor role in male-male competition. An important implication of musth and body size being stronger determinants of dominance than tusk possession is that it could facilitate rapid evolution of tuskless males in the population under artificial selection against tusked individuals, which are poached for ivory. (C) 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Heterospecific mating and species recognition in the planktonic marine copepods Temora stylifera and T. longicornis

Many planktonic copepods use diffusible pheromone or hydromechanical signals to remotely detect the presence of potential mates. To determine whether these mating signals also play a role in species recognition and mate choice, we observed and video recorded (3D) mate-finding and pursuit behaviors in heterospecific and conspecific mating crosses in a pair of congeneric, partially sympatric species (Temora stylifera and T. longicornis) in the laboratory. The species appear to have asymmetrical pre-mating isolation, with T. longicornis males readily pursuing T. stylifera females to mate contact and capture, but with little mate-finding activity observed in the reverse cross. Males of T. longicornis pursuing heterospecific females executed a number of behaviors known to facilitate successful pheromone trail following and mate capture in conspecific mating, including accelerated swimming in a ‘signal-scanning’ mode to recover a lost pheromone trail, reversal of the tracking direction in cases when the male initiated tracking in the incorrect direction, and accelerated swimming speeds when in the presence of a pheromone signal but prior to locating the trail. Detailed analyses of mate-tracking behavior in T. longicornis male × T. stylifera female crosses gave no indication that males were aware they were pursuing heterospecific females prior to mate contact, indicating that diffusible pheromone and hydromechanical signals are not used, either singly or in combination, for species recognition in this mating pair. Heterospecific mating attempts among sympatric, congeneric copepods may commonly proceed to mate capture, and incur fitness costs to either or both mating partners.

Responses to interactive playback predict future pairing success in nightingales

Birdsong is a sexually selected trait that serves in territory defence and mate choice. Individual song traits can be affected by the body condition of the male and thus may reflect his quality. Such relations between male quality and general singing performance raise the question whether differences in male quality also affect response strategies used in dyadic interactions. To address this question, we studied the relation between pairing success of male common nightingales, Luscinia megarhynchos, and their responses to rivals posing different levels of threat. Using interactive playback, we exposed males prior to mating to either aggressively or moderately singing rivals (by song overlapping and song alternating, respectively). Males that remained unpaired throughout the season (bachelors) interrupted their singing significantly more often after being overlapped than after alternating playback, whereas subsequently mated males kept the number of singing interruptions more constant across playback treatment. This suggests that subsequently paired males are less discriminative than are bachelors when challenged by rivals varying in aggressiveness. Regardless of playback treatment, males that later became paired responded significantly more strongly than did bachelor males. Thus, an increase in singing after a vocal interaction prior to mating predicted future mating success. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Early birds are sexy: male age, dawn song and extrapair paternity in blue tits, Cyanistes (formerly Parus) caeruleus

Sexual selection theory predicts that signals reflecting the relative quality of individuals should be used in mate choice. Females could base their choice of copulation partners on male secondary sexual traits that honestly signal male age, as predicted by the age-based indicator mechanism. Studies have shown that female blue tits prefer older males and that aspects of dawn song reflect male quality, but it remains unknown whether dawn song characteristics correlate with male age. We compared dawn song characteristics of second-year (SY) and older (ASY) male blue tits (cross-sectional analysis), and tested for age-related changes within individuals (longitudinal analysis) and differential overwinter survival of SY males. We further investigated the relation between dawn song and paternity gain and loss. We found that ASY male blue tits began to sing earlier relative to sunrise than did SY males. This difference in the onset of dawn singing was due to age-related changes in individual performance rather than differential survival of individuals with varying expression of the trait. Males that began to sing earlier at dawn had more mating partners, and were more likely to gain extrapair paternity. Our findings suggest that the onset of dawn song can provide a simple mechanism for females to assess the relative quality of their mate and of neighbouring males. We propose that females use the onset of singing as a cue for their choice of extrapair partners. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

The less amorous Gammarus: predation risk affects mating decisions in Gammarus duebeni (Amphipoda)

We examined the trade-off between the behaviours associated with predator avoidance and mate acquisition in the mate-guarding amphipod crustacean Gammarus duebeni. We used laboratory experiments to investigate the impact of olfactory predator cues on activity, mate choice and mate-guarding behaviour of males and females. Pair formation declined under perceived risk of predation, reflecting reduced activity of both males and females and hence a reduced likelihood of encountering a mate. We also observed a reduction in the choosiness of both males and females. Under increased perceived predation risk, assessment of the female by the male was more likely to be followed by pair formation, and males showed a nonsignificant trend towards reduced discrimination in favour of large females and were less tenacious in their pair bond when they paired during exposure to predator cues. Females also showed less resistance behaviour, suggesting that both males and females trade off the costs of maximizing current reproductive success against the benefits of predator avoidance for survival and reproduction in the future. We discuss the implications of such context-dependent mating behaviours for ecological interactions between species and suggest that predators, via the effects of perceived predation risk on mate choice and mate guarding in the prey species, induce trait-mediated indirect effects with the potential to influence population dynamics and community structure. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Aggressive responses to broadband trills are related to subsequent pairing success in nightingales

In sexually selected signals, distinct components often have specific signal value in mate choice or male-male competition. In songbirds, structural song traits such as trills, that is, a series of repetitive notes, can be important in female choice. However, little is known about their signal value in male-male interactions. Here, we investigated the hypothesis that males assess the competitive abilities of rivals based on the use and performance of rapid broadband trills produced within songs. Using a 2-speaker playback experiment, we exposed territorial male nightingales, Luscinia megarhynchos, that differed in their subsequent pairing success, to a simulated vocal interaction between 2 unfamiliar rivals. The singing of the 2 simulated rivals differed in the number of songs containing rapid broadband trills. Subjects responded significantly more strongly to the loudspeaker that broadcast songs containing such trills than to the loudspeaker that broadcast exclusively songs without such trills. Moreover, responses also depended on the fine structure of trills. Males that became paired later in the season significantly increased their response intensity with increasing trill performance, whereas males that remained unpaired responded in the opposite way and decreased their response intensity with increasing trill performance. These results indicate that rapid broadband trills are a signal of aggression and that the nature of the response in vocal interactions reflects aspects of the challenged male's fitness. © The Author 2008. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.


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Foraging ecology and parental behaviour in the common tern (Sterna hirundo)

One component of successful parenting is related to efficiency in foraging behaviour. The relationships among chick feeding, the size and type of food package, and length of parental foraging trips has not been well studied in seabirds. In addition, relatively few data have been collected on the activities of seabirds when foraging away from the nest site. The objectives of this study were: (1) to contrast productivity, feeding rate, and attendance patterns of individuals carrying a novel transmitter with a control group of birds; (2) to use radio-telemetry to assess the variability in foraging locations within and between individual male Common Terns; (3) to determine the seasonal variation in chick diet; (4) to determine for each transmittered bird, the relationships among the foraging patterns, parental behaviour, and seasonal reproductive success. The study took place over two years (1990-91) on a concrete breakwater 1 km offshore on Lake Erie near Port Colbome, Ontario. Ten pairs of terns in 1990 and 12 pairs in 1991 were radio-tracked by boat or car during the chick rearing stage. Concurrent behavioural observations documented the time each sex spent foraging or at the nest. The frequency and prey species composition of feeds to chicks were also recorded. The transmitters had negligible effects on the feeding frequency and brood attendance patterns of transmitter carrying birds. Peak nesting transmittered birds in 1990 and 1991 exhibited some inter-individual variability in foraging locations, however intraindividual variability was low. Birds foraged primarily to the west and northwest of the colony. Late nesters exhibited greater inter-individual variability, however intra-individual variability remained low for most birds. Neither group demonstrated sufficient variability to support the regular use of this colony as an "information centre". Individual transmittered birds had unique and predictable foraging patterns, and corresponding differences in feeding frequencies and brood attendance patterns, yet productivity was essentially equal between nests due to the impact and importance of stochastic events. Individuals that were recaptured in 1991 exhibited very similar foraging patterns to 1990, suggesting littie variability between years. Conservation of foraging patterns between years may have potential implications for mate choice decisions in future breeding seasons. Prey species delivered to chicks differed between morning and evening for peak and late nesters in 1990, but not 1991. Peak nesters in 1990 fed significantiy more Rainbow Smelt fOsmerus mordM) than Emerald Shiner (Notropis atherinoidesV this trend was reversed for late nesters who also fed large numbers of unidentified larval fish. No significant differences were found in 1991. Seasonal changes in prey species delivered to chicks is believed to be attributable to the temperature tolerances of the smelt and shiners, and the presence of large schools of larval fish during the late nesting season.

The effect of diet and parasite load on female phonotaxis in the Texas field cricket, Gryllus integer

Female crickets respond selectively to variations in species-specific male calling songs. This selectivity has been shown to be age-dependent; older females are less choosy. However, female quality should also affect female selectivity. The effect of female quality on mate choice was examined in Gryllus integer by comparing the phonotactic responses of females on different diets and with different parasite loads to various synthetic models of conspecific calling song. Test females were virgin, 11-14 days old, and had been maintained on one of five diets varying in protein and fat content. Phonotaxis was quantified using a non-compensating Kugel treadmill which generates vector scores incorporating the speed and direction of movement of each female. Test females were presented with four calling song models which differed in pulse rate, but were still within the natural range of the species for the experimental temperature. After testing, females were dissected and the number of gregarine parasites within the digestive tract counted. There were no significant effects of either diet or parasitism on female motivation to mate although the combined effects of these variables seem to have an effect with no apparent trend. Control females did not discriminate among song types, but there was a trend of female preferences for lower pulse rates which are closest to the mean pulse rate for the species. Heavily parasitized females did not discriminate among pulse rates altho~gh there was a similar trend of high vector scores for low pulse rates. Diet, however, affected selectivity with poorly-fed females showing significantly high vector scores for pulse rates near the species mean. Such findings raise interesting questions about energy allocation and costs and risks of phonotaxis and mate choice in acoustic Orthoptera. These results are discussed in terms of sexual selection and female mate choice.

Utilisation de l'information sociale, ses effets sur le choix du partenaire et le maintien des couples chez les oiseaux monogames : le cas du diamant mandarin (Taeniopygia guttata)

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Les effets de la présence d’une audience et de la condition sur les préférences d’appariement des femelles diamant mandarin (Taeniopygia guttata)

Le choix de partenaire est souvent considéré comme étant le résultat d’une simple interaction, mais, en nature, l’environnement social dans lequel les animaux communiquent correspond généralement à un réseau d’émetteurs et de récepteurs. La présence de congénères, de rivaux, et même de prédateurs durant le choix de partenaire peut avoir plusieurs répercussions sur ce choix. Être observé par une audience composée de congénères de même sexe peut pousser certaines espèces à modifier le niveau d’expression de leurs préférences, et même à modifier ces préférences pour réduire la compétition ou éviter d’être imitées. La préférence de plusieurs femelles diamant mandarin pour deux mâles a été mesurée en absence et en présence d’une audience femelle pour déterminer si la présence de rivales a des effets sur le choix de partenaire des femelles. De plus, afin de déterminer si ces effets varient en fonction de la qualité des femelles focales et audience, la condition de plusieurs femelles a été altérée en diminuant leur capacité à voler. Selon les résultats, les femelles diminuent leur niveau de sélectivité suite à l’ajout d’une audience femelle, et l’intensité des interactions mâle-femelle dépend de la condition des femelles focales. Les femelles ajustent leur comportement surtout pour éviter d’être imitées et non en fonction de leur condition. Cependant, ces deux mécanismes peuvent affecter les femelles simultanément.

Variations interindividuelles des performances cognitives et conséquences évolutives chez une population naturelle de mésange charbonnière (Parus major)

Les animaux font face à des changements environnementaux brutaux dus aux modifications de milieux liés à l'activité humaine et aux changements climatiques, et doivent s'ajuster rapidement à leur nouvel environnement. Certains processus cognitifs comme l'innovation et l'apprentissage permettent aux animaux d'intégrer de nouveaux comportements à leur répertoire comportemental (flexibilité comportementale), leur donnant l'opportunité d'intégrer un comportement plus optimal pour s'ajuster. Les performances cognitives varient entre espèces et les individus d'une même population et bien que des études récentes se soient intéressées aux causes des variations interindividuelles des performances cognitives, les conséquences restent peu explorées. Dans cette thèse, les questions des pressions de sélection s'exerçant sur les capacités cognitives sont abordées afin de mieux comprendre l'évolution de ces traits au sein d'une population naturelle de mésange charbonnière Parus major. Un nouveau test de résolution de problème a tout d'abord été présenté à des couples reproducteurs directement en milieu naturel. Les résultats ont montré que les couples les plus performants à résoudre la tâche surpassaient les couples les moins performants sur plusieurs mesures de succès reproducteur. Afin de vérifier que la motivation à nourrir les poussins ne biaisait pas cette relation, la taille de nichée a ensuite été manipulée, ce qui n'a pas affecté la performance subséquente des parents. Les couples innovateurs démontraient un meilleur succès reproducteur quel que soit le changement de la taille de nichée subit, ce qui suggère que cette performance influence bien le succès de reproduction, et non l'inverse. De plus, les couples innovateurs approvisionnaient leurs poussins plus souvent que les couples non innovateurs, suggérant que les innovateurs pourraient exploiter leur habitat de façon plus optimale. Dans un troisième temps, plusieurs caractéristiques morphologiques, dont la coloration des plumes, ont été reliées aux performances de résolution de problème et d'apprentissage. Ces liens, bien que complexes et condition-dépendants, pourraient indiquer un rôle de ces performances lors de la sélection sexuelle. Enfin, afin de tester l'effet du parasite sanguin du paludisme sur les traits comportementaux, un médicament contre le paludisme a été injecté à des femelles reproductrices. Cette injection n'a pas modifié leurs performances cognitives mais a augmenté leur niveau d'activité et d'exploration du nichoir en réponse à la tâche de résolution de problème. Ce parasite sanguin, très présent chez les populations depassereaux, pourrait donc expliquer les variations interindividuelles et interpopulationnelles de certains traits comportementaux en milieu naturel, au même titre que dans nombreux autres systèmes hôte-parasites étudiés. Les travaux présentés dans cette thèse ont permis de détailler pour la première fois la relation entre une performance cognitive et le succès reproducteur chez une population aviaire naturelle, une relation robuste et non influencée par la motivation à nourrir la couvée. Cette performance cognitive est reliée à plusieurs traits morphologiques, mais non à la charge parasitaire. Une meilleure exploitation de l'habitat et habileté à s'occuper des poussins pourrait expliquer cette relation.