Typically, as an animal's body grows, the individual parts of the body increase in size at different rates. This relationship between the growth of body parts and the whole body is a phenomenon called "growth allometry." Allometry of body parts may reflect the existence of resource limitations or a loss of functional demand, causing different body parts to develop at different rates and sizes as the organism gets larger. My project is a part of a larger study, geared towards the relationship between feeding habits, learning ability, and the structure of the brain in threespine stickleback, Gasterosteus aculeatus. We are interested in growth allometry of the brain both to take into account in comparisons between populations and because it may provide clues into the reasons for differences in brain shape among adults of ecologically contrasting populations.

The threespine stickleback are a morphologically diverse species widely distributed in temperate and boreal regions of the northern hemisphere. Extreme morphological variation occurs both within and among populations of threespine stickleback, and differences among populations are related to diet and predation. While stickleback eat a variety of prey, certain populations (benthics) are specialized in eating large, bottom prey, and other population (limnetics) are specialized in eating zooplankton.

The focus of my study concerns the changes in shape of the brain in one population that specializes on benthic prey. Specimens, indigenous to Cook Inlet, Alaska, were fixed in Alaska in 10% formalin in 0.1 M phosphate buffer and shipped to the laboratory at Stony Brook. A sample size of 30 female specimens from a wide range of sizes were chosen to eliminate the sex variable in my results. Digital images of lateral and dorsal views of the body were taken prior to brain extraction. Standard length (from tip of snout to base of tail) and eye diameter measurements were recorded with digital calipers before extractions. The digital images will be studied later using TPS software to analyze the quantified relationship between head shape and brain shape.

Three hours prior to extraction, specimens were soaked in 0.1 M phosphate buffer to reduce formalin concentration. Brain extractions took place in a fume hood under a dissecting microscope using a scalpel and forceps. Superficial tissue and skull bones were scraped away to expose the olfactory tract. The olfactory tract was gently detached from surrounding tissues. Once the dorsal view of the brain is exposed the extraction process continues ventrally through the roof of the mouth until the base of the skull was exposed. Then the remaining cranial nerves and spinal cord were severed, keeping the brain intact. The extracted brain was returned to 10% formalin in 0.1 M phosphate buffer. A digital image of the brain will be captured and used to measure brain shape. The growth allometry between brain shape, body shape and size will be analyzed using TPS and other statistical software. My project will be used for further analysis in concurrent studies occurring within the lab. A histological analysis will be conducted to see if differences in shape reflect a proliferation of specific types of brain cells possibly related to spatial learning and memory.