Braod Habits of Two Subspecies of a Freshwater Shrimp, Paratya compressa (Decapoda, Atyidae) and their Geographical Variations

Abstract

The concept of ‘brood habit’ recently proposed has been introduced in the examination of two subspecies of Paratya compressa. The pattern of brood habit within a population in compressa shows that egg size, relative brood size (RBS) and relative brood weight (RBW) remain almost similar regardless of body size, whereas in a population of improvisa egg size and RBW slightly increase with body size and RBS remains constant.The remarkable feature in brood habit among populations of the subspecies compressa is the presence of two distinct population groups that exhibit a varying series separately for mean egg size, mean RBS and mean brood size in relation to mean female body size, and the subspecies improvisa is included at the remote end of one series. The validity of these subspecies is doubted, by taking into account their distributional and morphological features as well, and two forms, improvisa-compressa complex (large-egg form) and the part of compressa (small-egg form) are shown recognizable. A geographical trend is noticeable in the variation of brood habit for each form, that can be considered as related to the adaptive strategy of increasing egg and body size near the border of species distribution range. © 1981, The Japanese Society of Limnology. All rights reserved.