The Adaptive Radiation of Cichlid Fish in Lake Tanganyika: A Morphological Perspective

Lake Tanganyika is the oldest of the Great Ancient Lakes in the East Africa. This lake harbours about 250 species of cichlid fish, which are highly diverse in terms of morphology, behaviour, and ecology. Lake Tanganyika's cichlid diversity has evolved through explosive speciation and is treated as a textbook example of adaptive radiation, the rapid differentiation of a single ancestor into an array of species that differ in traits used to exploit their environments and resources. To elucidate the processes and mechanisms underlying the rapid speciation and adaptive radiation of Lake Tanganyika's cichlid species assemblage it is important to integrate evidence from several lines of research. Great efforts have been, are, and certainly will be taken to solve the mystery of how so many cichlid species evolved in so little time. In the present review, we summarize morphological studies that relate to the adaptive radiation of Lake Tanganyika's cichlids and highlight their importance for understanding the process of adaptive radiation

The Utility of Geometric Morphometrics to Elucidate Pathways of Cichlid Fish Evolution

Fishes of the family Cichlidae are famous for their spectacular species flocks and therefore constitute a model system for the study of the pathways of adaptive radiation. Their radiation is connected to trophic specialization, manifested in dentition, head morphology, and body shape. Geometric morphometric methods have been established as efficient tools to quantify such differences in overall body shape or in particular morphological structures and meanwhile found wide application in evolutionary biology. As a common feature, these approaches define and analyze coordinates of anatomical landmarks, rather than traditional counts or measurements. Geometric morphometric methods have several merits compared to traditional morphometrics, particularly for the distinction and analysis of closely related entities. Cichlid evolutionary research benefits from the efficiency of data acquisition, the manifold opportunities of analyses, and the potential to visualize shape changes of those landmark-based methods. This paper briefly introduces to the concepts and methods of geometric morphometrics and presents a selection of publications where those techniques have been successfully applied to various aspects of cichlid fish diversification

Laterality strength is linked to stress reactivity in Port Jackson sharks (Heterodontus portusjacksoni)

Cerebral lateralization is an evolutionarily deep-rooted trait, ubiquitous among the vertebrates and present even in some invertebrates. Despite the advantages of cerebral lateralization in enhancing cognition and facilitating greater social cohesion, large within population laterality variation exists in many animal species. It is proposed that this variation is maintained due links with inter-individual personality trait differences. Here we explored for lateralization in Port Jackson sharks (Heterodontus portusjacksoni) using T-maze turn and rotational swimming tasks. Additionally, we explored for a link between personality traits, boldness and stress reactivity, and cerebral lateralization. Sharks demonstrated large individual and sex biased laterality variation, with females demonstrating greater lateralization than males overall. Stress reactivity, but not boldness, was found to significantly correlate with lateralization strength. Stronger lateralized individuals were more reactive to stress. Demonstrating laterality in elasmobranchs for the first time indicates ancient evolutionary roots of vertebrate lateralization approximately 240 million years old. Greater lateralization in female elasmobranchs may be related enhancing females’ ability to process multiple stimuli during mating, which could increase survivability and facilitate insemination. Despite contrasting evidence in teleost fishes, the results of this study suggest that stress reactivity, and other personality traits, may be linked to variation in lateralization

Motor activity of Daphnia magna (Crustacea, Cladocera) during thermal selection: Peculiarities of search reactions in the non-uniform environment

We conducted a study of the peculiarities of the motor activity of juvenile and adult individuals of Daphnia magna in the process of thermal selection. On the example of Daphnia, we experimentally proved the assumption that the decrease in the motor activity of the ectotherms in the selected temperature range is a behaviour mechanism typical for thermal selection. The experiment was conducted on the offspring of one parthenogenetic female (pure line) of a laboratory culture maintained over several years at room temperature. The Daphnia individuals had been beforehand acclimated over several generations to 23.4 ºС, and then were placed in a thermogradient apparatus. The control individuals were maintained at room temperature. The final temperature preference was determined using the so-called "chronic" method, when the tested organisms are maintained in a thermogradient apparatus over several days. The positions of the Daphnia individuals were recorded daily during 24 days. As a parameter which would characterize the motor activity of Daphnia, we used the parameter of average relative shifting, which was calculated as a difference (in cm) between the position they were found in two sequential records, divided by time (in min) between these records. Over the first 3 days, in the conditions of the temperature gradient, the Daphnia mostly selected heightened temperatures (24–28 ºС). During the period from the 4th to 24th day, 74% of the Daphnia selected the range of 18–23 ºС and 85% – 17–24 ºС. Thus, the range of the ultimate selected temperatures decreased by 4 ºС compared to the initially selected temperatures and enlarged by 3 ºС towards the lower temperatures. In the thermogradient apparatus, the parthenogenetic females had the lowest value of the mean relative movement. In the control, at room temperature, this parameter of the adults was by 43% higher compared to the gradient. The pattern of the dynamic of the indicator in both variants of the experiment was similar for the periods and phases of fluctuations. With the juveniles the value of the parameter of mean relative shifting in the gradient was higher by 40% compared to the adult Daphnia, but close to the parameter of the adults in the control. We determined a relationship between the juveniles selecting the higher temperatures and higher mean relative shifting, which indicates a relationship between the behavioural selective reaction of juvenile Daphnia and general physiological condition of their organism. During the absence of the temperature gradient, the Daphnia were observed to show symmetry in their motor reaction. Occurrence of the asymmetry of the motor reaction of the Daphnia in the condition of the thermogradient, manifesting in the prevalence of shifting to lower or higher temperatures, can indicate more clearly manifested search reaction in the condition of a non-uniform environment

The mechanisms and consequences of oviposition decisions in the European bitterling

Oviposition-site decisions can have disproportionate effects on offspring survival and success, and while the effects of these decisions are frequently investigated, the processes underpinning these decisions and the cues used are often less well understood. The aim of this thesis was to understand the mechanisms associated with making oviposition decisions, and their consequences, using the European bitterling (Rhodeus amarus), a small freshwater fish that lays its eggs in the gills of freshwater mussels. Using an artificial mussel, females were shown to respond to dissolved oxygen, relating to offspring survival, while males attend to water flow velocity, with implications for sperm competition. Oviposition decisions by either sex were unaffected by olfactory cues associated with sperm release, though males and females were responsive to visual cues associated with ejaculation. An analysis of the placement of eggs within the mussel gills by females failed to show evidence of “handedness”, though there was a tendency to place eggs in a mussel’s inner gills, which may be adaptive in avoiding competition with the mussel’s embryos. Male response to oviposition sites showed inter-population variation, with males from a population with high levels of mean crowding showing an elevated frequency of mussel inspection and probability of ejaculation. Males also increased the frequency of mussel inspection in response to the presence of a gravid female, suggesting a role for sperm competition and fertility assurance. Social network analysis was used to investigate how male interactions affect oviposition decisions. This approach showed that male mating tactics could be understood by quantifying how males distributed their sperm among oviposition sites. Findings are discussed in the context of our understanding of the bitterling mating system and research on oviposition-site decisions

Laterality, reproduction and parental care : an investigation in fish

Cerebral lateralisation or ‘laterality’, the partitioning of different cognitive functions in specific brain hemispheres, is a selectively advantageous trait that can enhance cognition. The selective advantages of exhibiting laterality are hypothesised to be the primary selective force driving its widespread evolution in both vertebrate and invertebrate taxa. However, substantial variation persists within this trait, particularly between the sexes. The underlying drivers of this variation are poorly understood, with social behaviours, especially those tightly associated with fitness, having received little consideration in this regard. In this thesis, I explored the relationship between cerebral lateralisation at the behavioural level, andreproduction and reproductive social behaviours, specifically parental care.In the first section of this thesis (chapters 2 - 4), I investigated whether variation in laterality, particularly between the sexes, is associated with reproduction and the performance of reproductive behaviours. In chapter 2, I provide evidence that in a live bearing species (guppies, Poecilia reticulata) there is variation in the pattern of laterality exhibited between the sexes, whereby individual males are consistent in the expression of laterality across three different behavioural contexts, while females are not, and instead exhibit substantial within individual variation.In chapter 3, I showed that in a uniparental species (threespine stickleback, Gasterosteus aculeatus), variation in laterality both between the sexes and within a single sex was attributed to reproduction and variation in individuals experience of performing reproductive behaviours respectively. Males, the caring sex, were more strongly lateralised than the non-caring sex (females) during reproduction, and laterality was reduced outside of the breeding season in males. Additionally, males with experience of mating and performing parental care behaviours were more strongly lateralised than males absent in this experience.In chapter 4, I explored whether laterality and its associated costs and benefits vary in different social contexts, while reproductive and performing parental care and in a nonreproductive non-social state, in a biparental substrate brooding cichlid fish, Telmatochromis temporalis. While I demonstrate no variation in laterality in a reproductive and nonreproductive state, I identified a cost of exhibiting laterality, poorer performance in a task requiring communication and cooperation between the left and right brain hemispheres, that is consistent regardless of sex or social context.In the latter section of this thesis (chapters 5 and 6), I assessed laterality in a fitness related reproductive social behaviour, parental care. Specifically, I explored whether parental care behaviours are lateralised in T. temporalis (chapter 5) and whether any biases in such behaviours are flexible when the selective pressures thought to select for laterality are altered (chapter 6). I provide the first evidence that parental care behaviours, specifically brood defence behaviour and visual hemisphere use during care, are lateralised in fish (chapter 5), and report that lateral biases in parental care behaviours may be flexible under differing selective pressures, here social and predation pressures, that result from experimental removal of the female biparental parent (chapter 6).Together, my findings suggest that reproduction and reproductive behaviours, particularly parental care, represent key but previously unidentified drivers of variation in laterality both within a sex and between the sexes. These findings provide new insights that help further our understanding of how variation in cerebral lateralisation evolved and why it may be maintained

Gene(s) and individual feeding behavior: Exploring eco-evolutionary dynamics underlying left-right asymmetry in the scale-eating cichlid fish Perissodus microlepis

The scale‐eating cichlid fish Perissodus microlepis is a textbook example of bilateral asymmetry due to its left or right‐bending heads and of negative frequency‐dependent selection, which is proposed to maintain this stable polymorphism. The mechanisms that underlie this asymmetry remain elusive. Several studies had initially postulated a simple genetic basis for this trait, but this explanation has been questioned, particularly by reports observing a unimodal distribution of mouth shapes. We hypothesize that this unimodal distribution might be due to a combination of genetic and phenotypically plastic components. Here, we expanded on previous work by investigating a formerly identified candidate SNP associated to mouth laterality, documenting inter‐individual variation in feeding preference using stable isotope analyses, and testing their association with mouth asymmetry. Our results suggest that this polymorphism is influenced by both a polygenic basis and inter‐individual non‐genetic variation, possibly due to feeding experience, individual specialization, and intraspecific competition. We introduce a hypothesis potentially explaining the simultaneous maintenance of left, right, asymmetric and symmetric mouth phenotypes due to the interaction between diverse eco‐evolutionary dynamics including niche construction and balancing selection. Future studies will have to further tease apart the relative contribution of genetic and environmental factors and their interactions in an integrated fashion

The behaviour and ecology of the zebrafish, Danio rerio

Author Posting. © The Authors, 2008. This is the author's version of the work. It is posted here by permission of Cambridge Philosophical Society for personal use, not for redistribution. The definitive version was published in Biological Reviews 83 (2008): 13-34, doi:10.1111/j.1469-185X.2007.00030.x.The zebrafish is an important model organism in developmental genetics, neurophysiology and biomedicine, but little is known about its natural ecology and behaviour. It is a small, shoaling cyprinid, native to the flood-plains of the Indian subcontinent, where it is found in shallow, slow-flowing waters. Zebrafish are group spawners and egg scatterers, although females are choosy with respect to sites for oviposition and males defend territories around such sites. Laboratory studies of zebrafish behaviour have encompassed shoaling, foraging, reproduction, sensory perception and learning. These studies are reviewed in relation to the suitability of the zebrafish as a model for studies on cognition and learning, development, behavioural and evolutionary ecology, and behavioural genetics

Caught by a heatwave: effects on behavior, mate choice and life history.

Negli ultimi decenni le ondate di calore marine (MHW), effetto del cambiamento climatico, sono aumentate notevolmente. Inoltre, come riportato da numerosi studi, si prevede che questa tendenza continuerà in futuro nella quasi totalità dei bacini idrici. Numerosi lavori hanno evidenziato gli impatti che le MHW hanno sugli organismi marini, tuttavia la letteratura presenta ancora carenze per quanto riguarda gli effetti che questi eventi hanno sulla fauna ittica. Lo scopo di questo studio è quindi quello di valutare gli effetti che le MHW hanno su pesci teleostei per avere una migliore comprensione di come questi eventi possono influenzare la biodiversità marina. Per questo scopo ho utilizzato un pesce di acqua dolce, Poecilia reticulata. Specie d'acqua dolce/salmastra possono infatti essere modelli preziosi per studiare le MHW per la loro semplicità di stabulazione. Femmine gravide e giovanili sono stati sottoposti a un’ondata di calore artificiale a seguito della quale alcuni tratti di life history e comportamentali sono stati confrontati con quelli degli individui appartenenti al gruppo di controllo. Le ondate di calore hanno provocato una significativa diminuzione della fecondità delle femmine. Le femmine sottoposte all’ondata di calore hanno prodotto meno nidiate rispetto alle femmine di controllo, covate di dimensioni inferiori con periodi di gestazione più lunghi. Inoltre, le femmine sottoposte all’ondata di calore hanno presentato una mortalità significativamente maggiore rispetto al controllo. In seguito al primo parto, le femmine, nuovamente recettive, sono state sottoposte ad un test di motivazione sociale/sessuale in cui potevano scegliere se stare con femmine o con maschi. In queste condizioni le femmine sottoposte a ondata di calore hanno speso significativamente più tempo assieme ad altre femmine rispetto al gruppo di controllo. Per quanto riguarda l’esperimento con i giovanili questi non hanno presentato differenze significative tra individui trattati e individui di controllo per quanto riguarda dimensioni corporee, peso, indice di condizione corporea e mortalità. Il giorno successivo al trattamento termico i giovanili sono stati sottoposti a tre diversi test. Nel primo test è stato misurato il comportamento anti-predatorio in risposta a due stimoli differenti. In risposta ad uno stimolo visivo gli individui sottoposti all’ondata di calore si sono immobilizzati più spesso e più a lungo rispetto ai controlli. Quando sottoposti a stimolo chimico gli individui sottoposti all’ondata di calore hanno risposto in maniera analoga agli individui di controllo. Entrambi i gruppi hanno aumentato la tigmotassi, tuttavia, l’aumento è stato meno marcato nel gruppo sottoposto ad ondata di calore rispetto a quello di controllo. Il secondo test a cui sono stati sottoposti i giovanili era un test di cattura. In questo test non sono state riscontrate differenze tra il gruppo trattato con ondata di calore e il gruppo di controllo. Infine, i giovanili sono stati sottoposti ad un test che ne misurava la velocità critica di nuoto e la resistenza sfruttando la loro innata propensione a nuotare controcorrente. In questo caso non sono risultate differenze significative nella velocità critica di nuoto tra il gruppo sottoposto ad ondata di calore e il gruppo di controllo; tuttavia i due gruppi hanno differito nel tempo medio di resistenza avendo il gruppo di controllo tempi di resistenza maggiori. Da questo studio si evince che le ondate di calore hanno un forte impatto su molteplici caratteristiche, anche in una specie eutermica quale P. reticulata. Questo studio dimostra inoltre che le MHW possono avere effetti diversi su individui che si trovano in fasi di vita differenti. Le MHW si presentano quindi come una forte minaccia per la resilienza delle popolazioni e più in generale per la biodiversità ittica nel prossimo futuro