HOWARD LAB - MEMBERS

W. Edwin Harris | Jason E. Jannot | Krista A. Larson

W. Edwin Harris

    Allocation of time and energy to reproduction influences the physiology, morphology and behavior of both sexes. In this research, the causes and consequences of patterns of sperm allocation in males will be investigated. Historically, most research in this field has concentrated on egg production because an egg is more costly to produce than a sperm is. However, although sperm are smaller than eggs, each ejaculate of a male may contain enormous numbers of sperm. Recent research has revealed that reproductive resources for gamete production can be limited for males as well as for females in many species. Critical to patterns of sperm investment by males is the degree to which females mate with multiple males. Such multiple mating sets up intense competition among sperm of different males to fertilize the same ova. One consequence of such sperm competition is the production of large ejaculates. A dynamic program model developed by W. E. Harris has provided predictions for spermatophore allocation in the salamander, Ambystoma texanum. This species is highly suitable for such a study because within any breeding aggregation, each male may deposit 60+ spermatophores each containing many thousand sperm, and each female may induct 20+ spermatophores into their reproductive tract prior to egg deposition. Predictions from the dynamic program model will be tested using controlled laboratory experiments.

Jason E. Jannot

    The processes by which developmental pathways evolve, and conversely, the effects of developmental processes on the paths that evolution may take, has held the interest of developmental biologists, ecologists, evolutionary biologists, paleobiologists, and systematists for a long time. However, at the beginning of the 20th century, a rift was manifest between developmental biology and ecological and evolutionary studies. Our understanding of how the environment shapes development and the influence of development on phenotypic variation has been hampered by this historical split. Over the last twenty years, there has been renewed interest in understanding the evolution of organismal form, initiated by the 'reunification' of developmental biology with ecology and evolutionary biology.
    Several questions remain unanswered in this re-emerging field, however. I wish to address two questions in particular. First, how do developmental events and the timing of those events influence the range of phenotypes observed? Second, how do developmental trade-offs in the allocation of resources influence phenotypic and developmental outcomes? Historically, these questions fall under the conceptual umbrella of phenotypic plasticity. Phenotypic plasticity is the ability of a single genotype to produce more than one alternative phenotype (physiological, morphological, or behavioral) in response to environmental conditions. The primary tool used in understanding phenotypic plasticity is the reaction norm. The reaction norm of a trait is the response of a single genotype to a single environmental factor (simplest case). Reaction norms describe how development transforms a genotype into a phenotype under a given set of environmental conditions.
    Many organisms exhibit life cycles that incorporate discrete, morphologically, behaviorally, and ecologically distinct phases, termed complex life cycles (CLCs; e.g., insects, marine invertebrates, amphibians. The developmental events, timing, and plasticity during transitions between stages in a CLC (e.g., egg >larva >pupa > adult) can influence the physiology, morphology and behavior of subsequent stages.
    I am studying how developmental plasticity in relation to changes in resources during the larval stage influences developmental events, developmental timing, and adult morphological and behavioral phenotypes in the caddisfly, Limnephilus externus (Trichoptera: Limnephilidae). I chose caddisflies because they have CLC's , as well as, specific behavioral and life history traits appropriate for such a study.

Krista A. Larson

    Most studies of anuran mating behavior involve species that produce simple advertisement vocalizations containing a repeated note or trill that varies only in pitch, duration, and rate of emission. These calls are given by males during the breeding season and function in long-range attraction of females and in signaling presence and location to nearby rival males in a chorus. However, several anuran species produce complex advertisement calls consisting of multiple types of notes that vary in number and temporal order. Whether or not complex calls provide additional information to conspecifics, increase the attractiveness of callers to potential mates, or are related to speciation events is unknown.

Click above image to hear a northern leopard frog vocalization

    My research investigates the largely undescribed but complex vocalization system of the northern leopard frog (Rana pipiens). Preliminary observations suggest that males possess a large repertoire of advertisement calls that are produced in variable numbers and combinations during calling bouts. The goals of my research project are: (1) to describe and categorize the number of advertisement calls present in the vocal repertoire of leopard frog males, (2) to document the general context in which these calls are produced, and (3) to determine their function in breeding aggregations. To accomplish this, I have recorded advertisement calls of individual males from breeding choruses in Indiana and Minnesota. I am analyzing the spectral properties and temporal patterning of these calls, as well as examining differences in usage of calls at different spatial locations in the chorus. Additionally, I am conducting playback experiments to quantify how males and females respond to each of the different types of calls, thereby distinguishing those calls that are used in male-male interactions from those that are involved in mate attraction. With data obtained in these experiments, I hope to discover why such a complex vocalization system has evolved in this species. In addition, I hope to obtain information on the behavior and habitat requirements of leopard frogs that may be useful in reversing the present trends of population decline in this species that are common throughout the study area.