Biology Theses and Dissertations
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Item INSIGHTS IN ECOLOGY, BEHAVIOR, AND REPRODUCTION FROM VISUAL MODELS OF AFRICAN CICHLIDS(2024) Gonzalez, Zeke Martin; Carleton, Karen L; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sexual selection has long been proposed to have played an important role in the explosive speciation of east African cichlids. Further, it is known that visual signals are the most salient ones to cichlids when it comes to reproduction. However, studies examining visual signals such as egg spots and size have been historically difficult to conduct due to the relationship between such phenotypes and confounding variables like age. In addition, the results from such studies often conflict and do not highlight clear patterns and hypotheses. In this dissertation, I use a receptor noise limited (RNL) visual model of increasing complexity to examine the discriminability of important visual signals in cichlid ecology, behavior, and evolution. In determining whether cichlid egg spots are truly mimics of cichlids eggs, I quantified fish and egg reflectance and found that two cichlid species are unable to distinguish the colors of eggs and egg spots in the lighting of their natural habitat. In order to bring together these quantitative methodologies with behavioral data, I tested the viability of using virtual stimuli displayed on a monitor to robustly examine how various visual signals affect conspecific male aggression. I found that although the cichlid Metriaclima zebra responds to virtual stimuli with equal aggression as towards live fish, it also responds with equal aggression towards virtual stimuli that differ in egg spot presence, body color, movement, and size. This suggests that virtual stimuli are not useful for behavioral tests in this species. Finally, in order to examine the salience of egg spots and body color in the wild, I calculated chromatic distance as a function of viewing distance for cichlid body colors against biologically-relevant backgrounds, conspecific body colors, and heterospecific body colors. The study shows that M. zebra body colors are discriminable from the space light at up to 5 m, but from the rocks at shorter distance, though distances that are comparable to the spacing of male territories. This suggests that males should be able to discriminate potential conspecific rivals on their breeding territories. Additionally, the visual model shows that M. zebra is highly discriminable from yellow heterospecifics but not so from blue heterospecifics. This dissertation emphasizes the importance of avoiding human biases in studies of cichlid color vision and behavior.Item Removal of Bower Paint Reduces Mate Searching Females' Return Visitation to Male Bowers(2011) Hicks, Reimi Elizabeth; Borgia, Gerald; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The multifaceted courtship display of male satin bowerbirds (Ptilonorhynchus violaceus) involves several elements that have been studied in detail. However, one of their most unusual behaviors, bower painting, has received little attention. Here, I propose two hypotheses for the function of paint and use multiple approaches to test predictions made by these hypotheses. First, I assessed how natural variation in paint quantity is related to other display traits, male mating success and male physical condition. Also, I used experimental methods including a paint removal and paint transfer experiment to investigate how birds responded to changes in the quantity and quality of bower paint. I found that males with more paint had better overall bower display quality and that fewer females returned to and copulated with males whose paint was removed. These results suggest that females may assess paint quantity during mate searching and demonstrate that paint influences male attractiveness.Item Patterns of song and preference variation in Laupala cerasina and their evolutionary implications(2010) Grace, Jaime Leigh; Shaw, Kerry L; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Closely related species often differ conspicuously in secondary sexual characters, many of which may be shaped by sexual selection. Changes in these characters may directly influence speciation, since females use them to assess males and to choose a mate. I investigate the hypothesis that in closely related populations, divergence in preference for sexually selected characters may promote sexual isolation through assortative mating. Ultimately, if reproductive isolation is complete, this process of divergent sexual selection through preference divergence may result in the formation of new species. I have investigated the relationship between divergence in the pulse rate of male song and female preference for pulse rates in a group of Hawaiian crickets, Laupala cerasina. Within a population, males sing at a characteristic pulse rate, but males from different populations sing with significantly different pulse rates. The degree of population divergence is almost an order of magnitude less than that which distinguishes closely related species of Laupala. Using phonotaxis trials, I found that females show acoustic preferences for males whose pulse rates fall nearest to the population mean. Across populations, male pulse rates and female preferences are significantly correlated, suggesting that they are coevolving. I have demonstrated that females discriminate among songs whose pulse rates vary within the range of pulse rates found among neighboring populations. Furthermore, in choice trials, females prefer the songs of males from the same population to those from neighboring populations. These females also exhibit significant assortative mating based on their acoustic preferences. Divergence in female acoustic preference among populations thus provides a mechanism for generating and maintaining biodiversity through divergence in sexually selected characters used in mate choice.Item The effect of relatedness on mating behavior in the satin bowerbird (Ptilonorhynchus violaceus)(2010) Reynolds, Sheila Mayo; Borgia, Gerald; Braun, Michael J.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Behavior is a main component of sexual selection theory in which male competition and female mate choice influence the evolution of a species. Relatedness commonly affects behavioral interactions, but the potential for relatedness to influence sexual selection is often overlooked. Here I show that relatedness affects mating behaviors in satin bowerbirds. Bowerbirds are a model species for non-resource based mating systems in which males provide only sperm to females, and females are free to mate with their preferred males, typically resulting in high skews in male mating success. Males build stick structures (bowers) on the ground to attract, and copulate with, females. Males compete, in part, by destroying neighboring males' bowers. Females search among multiple adjacent bowers and then select subsets of these males for courtship and then copulation. Automated video monitoring of bowers allows identification of males that destroy bowers and females that visit bowers for courtship or copulation. Using microsatellite genetic markers to estimate relatedness, I show that paternity assignments based on observed copulations match the genetic sires of offspring, supporting the hypotheses that copulations occur only at bowers and that male reproductive success can be reliably estimated from observed copulations. Next, I report that competing males are less aggressive, in the form of bower destructions, towards relatives than non-relatives and that this restraining effect of relatedness on aggression favors the close spatial association of relatives' bowers. These results support the hypothesis that relatedness affects male competition and ability to maintain attractive displays for females. Lastly, I investigate the influence of relatedness on female mate choice. I show that females do not actively prefer or avoid relatives in mate choice. However, females bias the areas in which they search for mates to be inclusive of relatives and then mate randomly with respect to relatedness within their search areas, resulting in tendencies to mate with relatives in some years. This effect of relatedness on female mate searching may be due in part to the spatial association of related males, and highlights the influence of mate searching rather than active mate preferences on overall mate choice patterns.Item COGNITIVE PERFORMANCE AND THE EVOLUTION OF MULTIPLE BEHAVIORAL DISPLAY TRAITS(2010) Keagy, Jason Christopher; Borgia, Gerald; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Males of many species have complex behavioral sexual displays and it is possible that these displays indicate aspects about male quality because of their relationship with cognitive ability. However, the relationship between behavioral display traits, cognitive ability, and reproductive success has received little attention. Satin bowerbirds, Ptilonorhynchus violaceus, are an excellent species for studying this relationship because their complex male courtship suggests a selective advantage to individuals with superior cognitive abilities. Here I show that cognitive performance can have important effects on mating success and the quality of behavioral displays. First, I present males with two novel problem solving tests and find that males who are better at solving these problems have higher mating success, establishing a link between male cognitive ability and sexual attractiveness. Second, I add four additional cognitive tests to expand the diversity of cognitive abilities tested and construct two measures of general cognitive ability using these data: the scores from an analysis that best explains covariation among performance on the different cognitive tests (g), and the average rank score on these cognitive tests ("IQ"). I show that these measures of general cognitive ability, as well as the majority of the independent cognitive tests, are positively associated with mating success. Third, I construct a different composite measure of male cognitive ability using an analysis that determines the combination of cognitive traits that make males most successful in attracting females (f). I show that this measure is significantly associated with my measures of general cognitive ability, suggesting that evolution of cognitive ability in bowerbirds is possible if there is sufficient heritability. I construct three different aggregate measures of male display quality (produced from four behavioral display traits) and find that they are all associated with f and with mating success. Finally, I show some support for the hypothesis that separate display traits may indicate different aspects of male cognitive ability. These results suggest that behavioral display traits may have a special role in sexual selection because of their connection to cognitive ability. Overall, this research highlights the importance of considering the interrelationship between cognitive ability and sexual selection.Item MATING COSTS, MALE CHOICE DISPLACEMENT, AND THE EFFECTS ON HYBRIDIZATION AND SPECIATION IN THE HAWAIIAN CRICKET LAUPALA (SUBFAMILY:TRIGONIDIINAE)(2009) Jadin, Jenna; Shaw, Kerry L; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Contact zones between two closely-related species provide unique laboratories for studying the processes of speciation. This is because, within these zones, species barriers will be reinforced and speciation will reach completion, or the barriers will break down, causing the two species to become one. Which of these two alternatives will occur depends on the degree of genetic differentiation and behavioral isolation between the species. If there is significant and non-combinable genetic variation between species, but behavioral isolation between the two incipient taxa is incomplete and allows hybrid offspring to be produced, these hybrid offspring will have lower fitness relative to parental types and selection should act directly to eliminate those offspring and indirectly against parents with broad mating preferences or traits. If however the genetic architecture is similar and behavioral isolation is incomplete, the populations would be expected to turn into a hybrid swarm and eventually become one species. Patterns of behavioral isolation and genetic variation in several Laupala species pairs suggest that contact zones between closely related species are marked by conflicting patterns of behavioral isolation and genetic differentiation. Evidence also suggests that the complex courtship system of Laupala may allow male choice to play an important role in sexual selection and speciation. Therefore I tested several hypotheses about the genetic differentiation, sexual selection, and behavioral isolation in a contact zone between the closely-related and morphologically indistinguishable L. tantalus and L. pacifica species pair. First, by using the mitochondrial COI gene and AFLPs as genetic markers, I demonstrated that there appears to be mitochondrial DNA introgression between sympatric, but not allopatric congeners, which suggests contemporary hybridization in the contact zone. Next, I found that males experience post-mating resource-limitation and show a significant tendency to invest less into a second mating, however, their investment is dependent upon female size. Finally, I found that there is apparent displacement of male choice, decreased variation in spermatophore production, and asymmetrical mating isolation within the contact zone. This evidence all suggests that there is increased behavioral isolation in this contact zone, which may be consistent with a hypothesis of speciation by reinforcement. However, this evidence also suggests that male costs may result in male choice conflicting with other isolating mechanisms. If so, this study may be another putative case of reinforcement, or it may be an entirely novel report of conflicting selection pressures within a hybrid zone. I suggest that further studies are needed to measure hybrid fitness as well as to evaluate relative male and female mating costs within the complex mating system of this rapidly-diversifying genus.Item USE OF MOLECULAR TECHNIQUES TO ADDRESS THE EVOLUTION OF DISPLAY TRAITS IN THE PTILONORHYNCHIDAE AND OTHER PASSERIFORM SPECIES(2009) Zwiers, Paul; Borgia, Gerald; Fleischer, Robert; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tests of hypotheses addressing the evolution of complex traits have greatly benefited from advances in the field of molecular genetics. Current molecular techniques allow for the identification of genetic variability, useful in estimating genetic relatedness and potentially explaining phenotypic variation. Here I use molecular data to address the evolution of complex traits within the Ptilonorhynchidae and other Passeriformes. My estimation of a bowerbird molecular phylogeny suggests two highly unlikely scenarios of complex trait evolution (i.e. polygyny, bower construction, decoration use, etc.); either polygyny and complex display traits evolved in parallel, or monogamy evolved from non-resource based polygyny, a transition for which no unambiguous examples could be found, and complex traits evolved once and were lost. Molecular evidence also supports the existence of four Sericulus species, dating the radiation to coincide with the upheaval of the central New Guinea mountain range, and suggests plumage coloration may be a labile trait within this group and therefore a poor indicator of species relatedness. Use of ultraviolet (UV) signals in birds is hypothesized to associate with the ability to see UV wavelengths, a trait with a well-documented genetic basis (replacements at key amino acid positions in the short-wavelength-sensitive 1 (SWS1) opsin pigment influence pigment sensitivity and potentially color discrimination). UV signal use may alternatively evolve to match the local light environment. Results from bowerbirds suggest extreme differences in UV reflectance are due to light availability and not differences in UV vision because amino acid sequences in the bowerbirds were nearly identical. Expanding upon this study, I compared SWS1 opsin gene sequences from 134 passeriform species and plumage UV reflectance measurements from 91 of these species. Results from the molecular data are unprecedented; replacements at five amino acid positions are predicted to have occurred nearly simultaneously, suggesting a constraint on UV vision evolution. Additionally, species reflect most intensely in wavelengths to which they are predicted to be sensitive. These results suggest a constraint on UV vision may also constrain the evolution of UV signals in the Passeriformes. These studies highlight the usefulness of molecular data when testing hypothesis of species and trait evolution.Item The adaptive significance and prevalence of courtship feeding in Hawaiian swordtail crickets(2008-06-04) deCarvalho, Tagide; Shaw, Kerry; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Males of many insect species feed their partner during courtship and mating. Studies of male nutrient donation in various systems have established that nuptial feeding has evolved mostly through sexual selection. Although there is extensive diversity in form, the function of nuptial gifts is typically limited to either facilitating copulation or increasing ejaculate transfer, depending on the time at which the gift is consumed by females. Unlike other insects, the Hawaiian swordtail cricket Laupala (Gryllidae: Trigonidiinae) exhibits serial transfer of nuptial gifts. Males transfer multiple spermless 'micro' spermatophores over several hours before mating at the end of the day (i.e. before the transfer of a single sperm-containing 'macro' spermatophore). By experimental manipulation of male microspermatophore donation, I tested several hypotheses pertaining to the adaptive significance of nuptial gifts in this system. I found that microspermatophore transfer improves insemination, by causing the female reproductive tract to take in more sperm. This result reveals a previously undocumented function for premating nuptial gift donation among insects. Enhanced sperm transfer due to microspermatophore donation may represent male manipulation or an internal mechanism of post-copulatory choice by females. I also performed experimental manipulation of male photoperiod to investigate how time and gender influence nuptial gift production and mating behavior. I found that the timing of mating is limited in males but not females and that the time of pair formation has consequences for the degree of nuptial gift donation, which suggests that both mating timing and microspermatophore number is important for male reproductive success. Finally, I observed the mating behavior of several trigonidiine taxa for a comparative analysis of sexual behavior and found that other genera also utilize spermless microspermatophores, which suggests that microspermatophore donation may be a common nuptial gift strategy among swordtail crickets. The elaborate nuptial feeding behavior of Hawaiian swordtail crickets prior to mating represents a newly discovered strategy to increase male insemination success rather than mating success. Based on this unexpected result, it is worth exploring whether courtship behaviors in other cricket or insect mating systems have also evolved to increase sperm uptake.Item Trade-offs within and between sexual traits in stalk-eyed flies (Diptera: Diopsidae)(2006-06-05) Fry, Catherine L; Wilkinson, Gerald; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The allocation of limited resources to competing body parts during development may affect both the absolute and relative sizes of physical traits, creating potentially dramatic consequences for the evolution of morphology. While negative correlations between the sizes of body parts ("trade-offs") arising from the distribution of finite resources have long been anticipated, empirical support is relatively rare. In this study, I use two related species of stalk-eyed flies that differ in morphology to investigate whether eye-span exaggeration results in trade-offs with other body parts. One species, <em>Cyrtodiopsis dalmanni</em>, is sexually dimorphic, with males having exaggerated eye-span while the other, <em>C. quinqueguttata</em>, is sexually monomorphic with both sexes having approximately equivalent and relatively unexaggerated eye-span. I utilize complementary approaches including artificial selection, application of exogenous juvenile hormone, and diet manipulation to alter the absolute and relative length of the eye-stalks in order to reveal correlated changes in other physical traits. The results of these experiments suggest that exaggerated eye-span in male <em>C. dalmanni</em> is accompanied by a decrease in two other features of head morphology, eye-bulb size and eye-stalk width, as well as compromised testis growth and sperm production. No trade-offs were observed in females of either species or male <em>C. quinqueguttata</em>. These results are consistent with hormonally-mediated trade-offs arising from the allocation of limited resources to an exaggerated trait and suggest that those trade-offs may act as costs of developing exaggerated eye-span.Item Variable female preferences and the evolution of complex male displays in satin bowerbirds (Ptilonorhynchus violaceus)(2005-05-18) Coleman, Seth William; Borgia, Gerald; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Models of sexual selection suggest that females benefit from assessing male display traits to choose their mates, but little is known about how individual females use particular male traits in mate choice. Here I show age-specific use of male display traits by female satin bowerbirds. Male satin bowerbirds build specialized stick structures - bowers - for courtship and copulation, and decorate their bowers with objects collected from the environment. When a female arrives at a bower for courtship, males produce intense behavioral displays that can threaten females. Using a decoration augmentation experiment, I find that young females emphasize blue decorations in mate choice decisions, while old females emphasize male display intensity. These variable preferences support a novel hypothesis for the evolution of multiple male display traits. I find that age-specific preferences reflect age-related differences in female tolerance for intense male displays: young females do not tolerate high-intensity displays and are frequently startled during courtship, while old females actively solicit high-intensity displays, and are rarely startled by these displays. I find that the presence of blue decorations calms females, especially young females, though the reason for the calming effect remains unclear. I find age-related improvement in females' abilities to discriminate among males in mate choice resulting in young females choosing males with higher parasite loads than those males chosen by old females. Finally, I find that juvenile males assess the quality of adult male tutors' displays when deciding which adult males to visit for male-male courtship - the behavioral context in which young males learn their displays. This finding supports a novel hypothesis for display trait learning, and shows that juvenile males have evolved preferences used in tutor choice that parallel female mate choice preferences. Overall, my work shows that (i) multiple male display traits may evolve via variable female preferences, (ii) variable female preferences may reflect interactions between female psychology and the male display traits available for assessment, and (iii) preferences for exaggerated male display traits may be shared by both sexes, but expressed in sex-specific roles.