Browsing by Author "Rittschof, Daniel"

The evolution of reproductive strategies involves a complex calculus of costs and benefits to both parents and offspring. Many marine animals produce embryos packaged in tough egg capsules or gelatinous egg masses attached to benthic surfaces. While these egg structures can protect against environmental stresses, the packaging is energetically costly for parents to produce. In this series of studies, I examined a variety of ecological factors affecting the evolution of benthic development as a life history strategy. I used marine gastropods as my model system because they are incredibly diverse and abundant worldwide, and they exhibit a variety of reproductive and developmental strategies.

The first study examines predation on benthic egg masses. I investigated: 1) behavioral mechanisms of predation when embryos are targeted (rather than the whole egg mass); 2) the specific role of gelatinous matrix in predation. I hypothesized that gelatinous matrix does not facilitate predation. One study system was the sea slug Olea hansineensis, an obligate egg mass predator, feeding on the sea slug Haminoea vesicula. Olea fed intensely and efficiently on individual Haminoea embryos inside egg masses but showed no response to live embryos removed from gel, suggesting that gelatinous matrix enables predation. This may be due to mechanical support of the feeding predator by the matrix. However, Haminoea egg masses outnumber Olea by two orders of magnitude in the field, and each egg mass can contain many tens of thousands of embryos, so predation pressure on individuals is likely not strong. The second system involved the snail Nassarius vibex, a non-obligate egg mass predator, feeding on the polychaete worm Clymenella mucosa. Gel neither inhibits nor promotes embryo predation for Nassarius, but because it cannot target individual embryos inside an egg mass, its feeding is slow and inefficient, and feeding rates in the field are quite low. However, snails that compete with Nassarius for scavenged food have not been seen to eat egg masses in the field, leaving Nassarius free to exploit the resource. Overall, egg mass predation in these two systems likely benefits the predators much more than it negatively affects the prey. Thus, selection for environmentally protective aspects of egg mass production may be much stronger than selection for defense against predation.

In the second study, I examined desiccation resistance in intertidal egg masses made by Haminoea vesicula, which preferentially attaches its flat, ribbon-shaped egg masses to submerged substrata. Egg masses occasionally detach and become stranded on exposed sand at low tide. Unlike adults, the encased embryos cannot avoid desiccation by selectively moving about the habitat, and the egg mass shape has high surface-area-to-volume ratio that should make it prone to drying out. Thus, I hypothesized that the embryos would not survive stranding. I tested this by deploying individual egg masses of two age classes on exposed sand bars for the duration of low tide. After rehydration, embryos midway through development showed higher rates of survival than newly-laid embryos, though for both stages survival rates over 25% were frequently observed. Laboratory desiccation trials showed that >75% survival is possible in an egg mass that has lost 65% of its water weight, and some survival (<25%) was observed even after 83% water weight lost. Although many surviving embryos in both experiments showed damage, these data demonstrate that egg mass stranding is not necessarily fatal to embryos. They may be able to survive a far greater range of conditions than they normally encounter, compensating for their lack of ability to move. Also, desiccation tolerance of embryos may reduce pressure on parents to find optimal laying substrata.

The third study takes a big-picture approach to investigating the evolution of different developmental strategies in cone snails, the largest genus of marine invertebrates. Cone snail species hatch out of their capsules as either swimming larvae or non-dispersing forms, and their developmental mode has direct consequences for biogeographic patterns. Variability in life history strategies among taxa may be influenced by biological, environmental, or phylogenetic factors, or a combination of these. While most prior research has examined these factors singularly, my aim was to investigate the effects of a host of intrinsic, extrinsic, and historical factors on two fundamental aspects of life history: egg size and egg number. I used phylogenetic generalized least-squares regression models to examine relationships between these two egg traits and a variety of hypothesized intrinsic and extrinsic variables. Adult shell morphology and spatial variability in productivity and salinity across a species geographic range had the strongest effects on egg diameter and number of eggs per capsule. Phylogeny had no significant influence. Developmental mode in Conus appears to be influenced mostly by species-level adaptations and niche specificity rather than phylogenetic conservatism. Patterns of egg size and egg number appear to reflect energetic tradeoffs with body size and specific morphologies as well as adaptations to variable environments. Overall, this series of studies highlights the importance of organism-scale biotic and abiotic interactions in evolutionary patterns.

Reactive oxygen species (ROS) are produced endogenously in all aerobes and are induced by environmental stressors. ROS oxidize and disable essential cellular components such as DNA, proteins, and lipid membranes. Exposure to metals, polycyclic aromatic hydrocarbons (PAHs), and some pesticides can induce oxidative stress in marine invertebrates. All aerobic organisms have a network of antioxidants and enzymes to quench ROS and prevent oxidative damage. This dissertation examines antioxidant and oxidative stress biomarkers in endemic molluscs and crabs from two natural extreme environments: deep-sea hydrothermal vents in the Lau and North Fiji Basin, and cold seeps in the Gulf of Mexico. In addition, the acute toxicity and sub-lethal effects of four insecticides and an herbicide are examined in the estuarine blue crab, Callinectes sapidus. Blue crabs are North Carolina's most important fishery species and are frequently found in agricultural drainage ditches, an example of an anthropogenic extreme environment.

Total glutathione, catalase, superoxide dismutase, and lipid peroxidation levels were of the same respective order of magnitude in the two vent gastropods, Alviniconcha sp. and Ifremeria nautilei, and vent mussel, Bathymodiolus brevior. These biomarkers activities were similar to those from previous reports on Mid-Atlantic Ridge mussels, except for ~100-fold higher lipid peroxidation levels among Lau molluscs. Principal component analysis (PCA) of mollusc tissue-specific biomarker levels grouped individuals by species rather than by site.

Biomarker levels in the seep mussels Bathymodiolus childressi, B. brooksi, and B. heckerae were similar across species except for elevated foot and gill cytosolic SOD in mussels from MC-640 compared to those from AC-645. PCA of seep mussel biomarker levels differentiated by species with B. childressi isolated from B. brooksi and B. heckerae. The addition of B. brevior biomarker data to the PCA showed them grouping around B. brooksi and B. heckerae. Bathymodiolus childressi is ancestral to the other species and contains only methanotrophic endosymbionts. Whether symbionts play a role in alleviating possible toxic conditions remains unknown.

Pesticides were acutely toxic to blue crabs in the order of Lambda-cyhalothrin > imidacloprid ≈ aldicarb > acephate ≈ Roundup® (glyphosate). Megalopae were almost always more sensitive to pesticides than early stage juveniles. Commercial formations of pesticides generally showed similar toxicity to active ingredients alone. Exposure to LC₂₀ levels of acephate, aldicarb, imidacloprid and Roundup significantly increased the frequency of juvenile mortality after molting. There was no significant change in total glutathione or lipid peroxidation of exposed megalopae. Lambda-cyhalothrin-, imidacloprid-, and aldicarb-based products have the potential to cause acute toxicity and molting-related mortality in shallow creeks and ditches.

The focus of this dissertation is the extension of the innate immune response in wound healing and non-wound healing contexts. I am interested in interactions at the interface between macroorganisms and microorganisms from marine/aqueous environments. This dissertation explored two aspects of the interactions: 1) the presence and function of macroorganism secretions and 2) the role of secretions in managing microfouling on macroorganism surfaces. Particularly of interest are how barriers are biochemically reinforced to mitigate microfouling and the potential consequences of a breach in those barriers. The innate immune response, an evolutionary conserved system in vertebrates and invertebrates, provides an evolutionary context for developing the hypotheses.

In this dissertation the biochemical composition and uses of crustacean secretions are explored for barnacles, fiddler crabs and blue crabs. Fluids of interest were secretions released during barnacle settlement and metamorphosis and those collected from living adult barnacles, fluids on fiddler crab sensory appendages including dactyl washings and buccal secretions, and fluids from blue crab egg masses. The biochemical composition was determined using a combination of fluorescent probes and confocal microscopy, proteomics, and enzyme-specific substrates with a spectrophotometer.

I demonstrated that self-wounding is inherent to the critical period of settlement and metamorphosis, in barnacles. Wounding occurs during cuticle expansion and organization and generates proteinaceous secretions, which function as a secondary mode of attachment that facilitates the transition to a sessile juvenile. I showed extensive proteomic evidence for components of all categories of the innate immune response, especially coagulation and pathogen defense during attachment and metamorphosis. This work provides insight into wound healing mechanisms that facilitate coagulation of proteinaceous material and expands the knowledge of potential glue curing mechanisms in barnacles.

In order to test macroorganism secretions in a non-wound healing context, I examined fluids sampled from body parts that macroorganisms must keep free of microorganisms. I showed that two types of decapod crustaceans can physically manage microorganisms on most parts of their body, but certain parts are particularly sensitive or difficult to clean mechanically. I examined sensory regions on the fiddler crab, including dactyls that are important for chemoreception and the buccal cavity that is used to remove microorganisms from sand particles, and blue crab egg mass fluids that protect egg masses from fouling through embryo development.

This dissertation explores organismal interactions across scales in size, space, and time. The findings from the barnacle work inform mechanisms of attachment and glue curing, both central to understanding bioadhesion. The work on fiddler crabs and blue crabs contributes to our understanding of chemoreception of feeding and reproductive behaviors.

The work presented here highlights how biological secretions from macroorganisms serve multifaceted roles. In cases of physical breaches of barriers, or wounding, secretions coagulate to obstruct loss of hemolymph and have antimicrobial capabilities to prevent infection by microorganisms. In non-wounding cases, secretions remove microorganisms from surfaces, whether that is on the body of the macroorganism or in the immediate environment.