In this study, predation efficiency of three guppy ( Poecilia reticulata) size classes was evaluated at various vegetation densities in a series of circular aquaria containing plastic plants closely resembling Ceratophyllum demersum. The effect of vegetation density was most apparent among large fish where predation efficiency greatly diminished from 12.35 mosquito larvae (Aedes aegypti) to 4.68 as vegetation densities rose from 3 to 19 plants/700 cm2. Over that same range of increasing vegetation densities, predation among small fish remained unchanged, whereas among fish of intermediate size predation declined significantly but less precipitously than for large individuals. When presented with a choice between second and fourth mosquito larvae, small fish preferred to prey on second instars, whereas large fish preferred fourth instar larvae. Fish of intermediate size did not show a statistically significant preference. The functional response of fish to increasing prey densities, as measured over a 12-h period, was of Type III.

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Behavior may be dramatically influenced by changing environments, and differences in light intensity environments may have important behavioral consequences. One approach to understanding changes in behavior is by studying behavioral syndromes, suites of correlated behaviors reflecting between individual consistencies in behavior expressed within a behavioral situation (e.g., correlations between antipredator behaviors in different habitats), or across behavioral contexts (e.g., correlations among feeding, antipredator, or mating behavior) (Sih et al. 2004a). Guppies (Poecilia reticulata) provide a great model system to study behavior. Guppies are small, freshwater tropical fish that inhabit still pools in swift-flowing streams, and the backwaters of small rivers in mountain forest areas of Trinidad (Houde 1997; Magurran 2005). In this study I attempted to answer the following questions using three low predation populations of guppies : 1) Do guppies display a behavioral syndrome for aggression and/or courtship across light situations?; 2) Are there mean level changes in aggression or courtship across light situations?; 3) Are mean level changes influenced by differing social environments that include or lack sexually receptive females?; 4) Are there correlations between behavior and the androgen hormones testosterone and 11-ketotestosterone?; 5) Are there correlations between behavior and the stress hormone cortisol?; 6) Are there mean level changes in hormone release rates across light environments?; and 7) Is flexibility in hormone release rates influenced by social environments that include or lack sexually receptive females? Guppies exhibit behavioral syndromes for both aggression and courtship. Furthermore, guppies exhibit behavioral flexibility for both aggression and courtship, but only in social environments that include sexually receptive females. I found no correlations between behavior and androgen hormones. I also did not find any correlations between behavior and the stress hormone cortisol. Furthermore, I did not find any mean level changes in hormone release rates across light environments. Interestingly, cortisol levels were higher in social environments in which sexually receptive females were absent. Many studies have looked at how the environment influences courtship behavior in guppies, especially employing high predation populations, but few studies have examined aggressive behavior or behavior in general with low predation populations. Furthermore, few studies have determined the role social environments play, and how hormones may interact with behavior. This study is important because it helps illuminate how low predation populations deal with changes in light intensity environments, and adds to what we understand about guppy behavior in general.

Ecological speciation involves the evolution of reproductive isolation (RI) as a by-product of adaptation to different selective environments. Parallel patterns of non-random mating by environment type provide strong evidence that ecological speciation has occurred. The processes involved in the origins of RI are more difficult to detect however. One mechanism involves the correlated evolution of mating preferences and sexually selected traits. I developed a conceptual model for detecting RI under various scenarios of mate preference evolution. The model predicts that RI will not evolve if preferences are evolutionarily constrained relative to the preferred traits, but is detectable as long as preferences evolve in parallel. I then applied this framework to an empirical system with populations of guppies (Poecilia reticulata) adapted to low- and high-predation environments. I measured female mate preferences for male colour and size; traits which are divergent between the two environment types. Preference functions for colour also diverged in the predicted direction. The parallel pattern of preference divergence suggests that divergent natural selection from predators may be contributing to RI between guppy populations.

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The invasion of individuals into new habitats can pose a major threat to native species and to biodiversity itself. However, the consequences of invasions for native populations that are not fully reproductively isolated from their invaders are not yet well explored. Here I chose the Trinidadian guppy, Poecilia reticulata, to investigate how different population traits shaped the outcome of Haskins's introduction, a well-documented invasion of Guanapo river guppies into the Turure river. I especially concentrated on the importance of behaviour for invasive success. I investigated if the spread of Guanapo guppies is due to superiority in behaviour, life-history and/or genetics, or if the outcome of this translocation is due to chance. Despite the fact that by today the invasive front has passed the Turure's confluence with the River Quare many kilometres downstream of the introduction site, and the original genotype only survives in small percentages, as was revealed by genetic analysis in this and other studies, no obvious differences between invasive and native populations could be detected in any of the tested behavioural, life-history and genetic traits. When tested for mate choice, neither Guanapo nor Oropuche (Turure) males seemed to be able to distinguish between the population origin of females, but courted and mated at random. At the same time, females did not prefer to school with individuals of the same population over schooling with more distantly related females. The formation of mixed schools after an invasive event is therefore likely. Because female guppies showed a very low willingness to mate, even after having been separated from males for up to six months, sperm transfer through forced copulations will become more important. Taken together, these behaviours could increase the speed of population mixing after an invasion without the need for behavioural superiority of the invasive population. When tested for their schooling abilities, offspring of mixed parentage, in contrast to pure breds, displayed a large amount of variety in the time they spent schooling, a circumstance that can potentially influence survival rates and therefore the direction of gene pool mixing. Guanapo fish did not show reproductive superiority in a mesocosm experiment, where both populations were mixed in different proportions. On the contrary, in two out of three mixed treatments, the amount of Oropuche (Turure) alleles was significantly higher than expected from the proportion of initially stocked fish. The almost complete absence of distinguishable traits other than genetic variation between the examined populations that belong to different drainage systems, opposes the recent split of the guppy into two different species following drainage system borders, as is argued in this thesis. However, the successful invasion of the Turure by Guanapo guppies and the nearly entire disappearance of the original population can be explained in absence of differing population traits. Here I demonstrate how behavioural and genetic interactions between subspecies influence the outcome of biological invasions and second, how factors other than population traits, such as the geographic situation, can produce an advantageous situation for the invader even in the absence of population differences.

Made available in DSpace on 2016-08-10T10:39:23Z (GMT). No. of bitstreams: 1 Jefferson Mendes Gomide.pdf: 1020338 bytes, checksum: 0191262649084f3b90170c5b28b340dd (MD5) Previous issue date: 2008-12-17 / The invasion of new environments is related to the genetic variability of the species. The guppy (Poecilia reticulata) is a species introduced accidentally or artificially, arisen from different populations of captivity around the world. In some countries, these introductions are made repeatedly, particularly to control the growth of disease-transmitting mosquitoes in small lakes and streams in tropical countries. The Guppy is feeding the larvae of mosquitoes, preventing it from coming into adult life. Because of the need to obtain a better understanding of the differentiation of introduced populations, and this may reduce the impact of the introduction of exotic species, since it is the third leading cause of extinction of native species, three populations in different cities of the state of Goias were collected, and their metric features analyzed. The review sought to determine the rate of divergence among populations of free life, which contribute to the understanding of the process of colonization of natural environments by this alien species. The results indicated that the divergence between the populations analyzed, for most of the features is very large, ie the rate of divergence is greater than expected by neutral evolution, so that directional selection is expected to be acting on these characteristics. / A invasão de novos ambientes se relaciona com a variabilidade genética das espécies. O Guppy (Poecilia reticulata) é uma destas espécies introduzidas acidentalmente ou artificialmente, advindo de várias populações de cativeiro em todo o mundo. Em alguns países, estas introduções se deram várias vezes, particularmente para o controle do crescimento de mosquitos transmissores de doenças, em lagos e pequenos riachos nos países tropicais. O Guppy se alimenta das larvas desses mosquitos, impedindo que cheguem à fase adulta. Devido à necessidade de se obter uma maior compreensão da diferenciação de populações introduzidas, e com isto poder reduzir o impacto da introdução de espécies exóticas, já que é a terceira causa de extinção de espécies nativas, foram coletadas três populações em cidades diferentes do estado de Goiás, e as suas características métricas analisadas. A análise procurou determinar a taxa de divergência, entre populações de vida livre, que contribuirá para a compreensão do processo de colonização dos ambientes naturais por esta espécie exótica. Os resultados indicaram que a divergência entre as populações analisadas, para a maioria das características é muito grande, ou seja, a taxa de divergência é maior do que a esperada pela evolução neutra, de modo que seleção direcional deve estar atuando sobre estas características.

Background: Multidirectional interactions in social networks can have a profound effect on mate choice behavior; e.g., Poecilia mexicana males show weaker expression of mating preferences when being observed by a rival. This may be an adaptation to reduce sperm competition risk, which arises because commonly preferred female phenotypes will receive attention also from surrounding males, and/or because other males can copy the focal male's mate choice. Do P. mexicana males indeed respond to perceived sperm competition risk? We gave males a choice between two females and repeated the tests under one of the following conditions: (1) an empty transparent cylinder was presented (control); (2) another ("audience") male inside the cylinder observed the focal male throughout the 2nd part, or (3) the audience male was presented only before the tests, but could not eavesdrop during the actual choice tests (non-specific sperm competition risk treatments); (4) the focal male could see a rival male interact sexually with the previously preferred, or (5) with the non-preferred female before the 2nd part of the tests (specific sperm competition risk treatments). Results: The strength of individual male preferences declined slightly also during the control treatment (1). However, this decrease was more than two-fold stronger in audience treatment (2), i.e., with non-specific sperm competition risk including the possibility for visual eavesdropping by the audience male. No audience effect was found in treatments (3) and (5), but a weak effect was also observed when the focal male had seen the previously preferred female sexually interact with a rival male (treatment 4; specific sperm competition risk). Conclusion: When comparing the two 'non-specific sperm competition risk' treatments, a very strong effect was found only when the audience male could actually observe the focal male during mate choice [treatment (2)]. This suggests that focal males indeed attempt to conceal their mating preferences so as to prevent surrounding males from copying their mate choice. When there is no potential for eavesdropping [treatment (3)], non-specific specific sperm competition risk seems to play a minor or no role. Our results also show that P. mexicana males tend to share their mating effort more equally among females when the resource value of their previously preferred mate decreases after mating with a rival male (perceived specific sperm competition risk), but this effect is comparatively weak.

Comparisons of functionally important changes at the molecular level in model systems have identified key adaptations driving isolation and speciation. For example, recent studies suggest mutations in opsins, the genes that encode retinal photoreceptors, influence colour-based female mate choice and have, thereby, contributed to the radiation of African cichlids. To test the hypothesis that the evolution of elaborate colouration in guppies (Poecilia reticulata) is also associated with opsin gene diversity, long wavelength-sensitive (LWS) opsin genes were sequenced in six species of the family Poeciliidae. Sequences of four LWS genes were amplified from the guppy genome and from mRNA isolated from adult eyes. Variation in expression was quantified using qPCR. Three of the four paralogs encode opsins that appear to be most sensitive to different wavelengths of light, as they vary at key amino acid positions. This family of LWS opsin genes was produced by a diversity of duplication events. One gene appears to be the product of retrotransposition. Between-gene PCR and DNA sequencing show that two of the guppy LWS opsins are linked in an inverted orientation. The fourth locus is a hybrid, with the first five exons most similar to one of the tandem duplicates and the last exon most similar to the other. The single-exon LWS opsin was produced prior to the divergence of families Fundulidae and Poeciliidae. The inverted tandem duplication event occurred near the base of the poecilid tree, in the common ancestor of Poecilia and Xiphophorus, and the hybrid locus is found only in the genus Poecilia. Enhanced wavelength discrimination, a likely consequence of opsin gene duplication and divergence, might have been an evolutionary prerequisite for colour based sexual selection and have led to the extraordinary colouration now observed in male guppies and in many other poeciliids.