Biology
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Item A comparative analysis of sperm storage in six brachyuran superfamilies: mating behavior, ecological variation and phylogenetic patterns(2010) Rodgers, Paula Jane; Reaka, Marjorie L; Hines, Anson H; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While life history traits are shaped by allometric, phylogenetic, environmental and behavioral factors, few comparative studies of brachyuran life history patterns have considered sperm storage traits as important components of reproductive strategies. To understand the evolutionary forces selecting for sperm storage and their interactions with other life history traits, I (1) used controlled laboratory experiments and field mating observations to examine variation in male sperm transfer patterns, (2) sampled variation in female reproductive output and sperm storage for two species across a latitudinal gradient, (3) conducted a survey of life history traits across a broad range of brachyuran taxa, and (4) used phylogenetic analyses to identify patterns in the evolution of life history traits in brachyurans. From mating experiments and observations on five species, I found that males transfer more sperm with longer than shorter copulation durations and that variation in copulation duration was shaped by differences in the species' ecologies. Latitudinal surveys of two species with contrasting mating systems identified seasonal and geographical variation in female reproductive output. While the variation in most reproductive traits could best be explained at smaller spatial scales, a sperm storing species, Callinectes sapidus became sperm limited at low latitudes. From a comparative survey of male and female life history traits across 61 species of brachyurans, I found that allometry, phylogeny and mating strategies explained much of the variation in life history traits. Using rigorous phylogenetic techniques, male life history traits showed more plasticity across the phylogeny than female traits suggesting male traits may be influenced more by behavioral and environmental factors. After correcting for phylogenetic signals, species with larger male sperm stores had larger amounts of sperm stored by the female. In summary this dissertation illustrates the importance of partitioning variation in mating behavior, phylogeny, environmental factors and allometry when examining the evolution of life history traits in brachyurans.Item Die Balz des Kolibris Selasphorus platycercus(Zoologische Jahrbücher. Abteilung für Systematic, Ökologie, und Geographie der Tiere, 1948) Wagner, H. O.; Inouye, David W.This article describes behavior of Broad-tailed Hummingbirds (Selasphorus platycercus) in Mexico, which the author describes (perhaps mistakenly) as mating behavior.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 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.