Comparison of two sweet-water shrimps from puerto rico: morphological differences and feeding behavior

Mechanistic bases of behavior:

Comparison of two sweet-water shrimps from Puerto Rico: morphological differences and feeding behavior

Department of Biology
University of Puerto Rico
Rio Piedras, Puerto Rico 00931

Mechanistic bases of behavior:
ABSTRACT
We studied two species of freshwater shrimp, Atya innocous and A. larilpes in order to assess if differences feeding behavior arerelated to differences in morphology. Our findings indicate that most individuals of Atya Ianipes do not feed at 500 ml! 5 sec. flow rate, and 500 ml/3 sec. The data for Atya innocous indicate a similar pattern in feeding behavior at a flow rate of 500 mlI:5 sec However, the number of filter feeding individuals increase at 500 mI!3 sec. flow rate.
Morphological data indicate no differences in bodylength between species, although, A. innocous is slightly larger in size than A. !anipes. However, we found interspecific differences in femur thickness with Atya innocous having a thicker femur than Atya Ianipes. This morphological specialization is though to be important for resource partitioning because it allows Atya irinocous to exploit a feeding niche (high flow rates in the upstream region)unavailable to A. ianipes in the aquatic community. Therefore, coexistence of both species is though to be possible because of morphological specialization which allows species to utilize effectively a different set of food and space resources.

Mechanistic bases of behavior:
INTRODUCTION
The shrimps Atya Thnocous and A. lanipes (Decapoda, Atyidae) coexist and are widespread in streams andrivers in Puerto Rico (Párez Reyes 1999). This distribution probably has to do with exploitation of wide range of detritous and animal food resources by use of speclaflzed appendages or chela (Fryer 1977). In these shrimps the dactili and the propodi of the first two periopods are modified with long setae that the animal uses to scrape rock surfaces or filter water column Pringle, et $1. 1993.)There are morphological differences between the two species, with A, innocous being the more robust and larger of the two. In A. Ianipes all walking legs are the same size, whereas the first pair of walking legs in A. innocous are thicker. This specialization was thought to be important for resource partitioning by allowing A. innocous individuals to be able to hold on even high flow rates in theupstream region. However, distribution data indicate no differences for the two species either for different streams, or different elevations or different microhabitats (Perez Reyes 1999). Nevertheless, individuals in the same location may differ in the use of these sites,
Here we examine if differences in morphology between A. lanipes and A. innocous are behind their difference in feeding behaviorIf their differences in feeding behavior are related to microhabitat, thr may indicate that coexistence of both species is possible because of resource partitioning of food resources.

J Mechanistic bases of behavior:
METHODS
We recorded two types of data in this experiment, observations of feeding behavior and morphometric measurements. In the feeding observations we placed 20 individuals ofAtya lanipes in a shrimp aquarium with no water flow (the pump turned off) and let them acclimate for 15 minutes. After shrimps acclimated we recorded the distribution of individuals in the aquarium and their feeding behavior. Three types of feeding behaviors were observed, filter feedingscraping the surface, and not feeding. After colleàting initial data on distribution and feeding behavior weturn on the pump and calibrate the water flow rate at 500 ml/15 sec. and waited for 15 minutes for the shrimp to acclimate and collect feeding behavior observations. Once the second set of observations was completed we re-calibrate water flow to 500 ml/5 sec. and repeated the sampling protocol. After all data on A. !anipes was recorded the shrimps were returned to the holding tank and the sampling...