Form alternation of adult female crayfishes of the genus Orconectes (Decapoda: Cambaridae)

Adult female Orconectes illinoiensis, O. indianrnsis, O. kentuckiensis, O. cf. propinquus and O. virilis were investigated for evidence of form alternation similar to that in conspecific males. Living females were categorized qualitatively as form I or form II. Form I females exhibited one of the following, swollen white glair glands, dependent offspring (embryos to 3(rd) instar juveniles) or eggstalks with remnants of eggs attached to pleopods, All other females were classified as form II. Only form I females were observed mating with form I males, therefore the form I condition is considered to be sexually active. Quantitative differences were observable for living and preserved specimens for carapace length to pleonite 2 width ratio (CL/P). Form I females have wider abdomens and a lower CL/P ratio than same-sized form II female conspecifics. Form II females are most prevalent during the summer growing season. Form I females first appear in the fall mating season and are the most abundant female form through the end of the spring spawning season for females of adult dimensions, Six female O. illinoiensis collected in the late growing season as form 11 of minimum adult dimensions or greater and nine collected in berry (form I) during the spring spawning season were held under natural photoperiod for instar advancement. All six females collected in early, fall as form II molted into a form I instar while 8 of 9 collected in spring as form T (in berry) molted into a form II instar. Two females collected as form I molted into a form I instar after a single intervening form II instar while one female proceeded through 2 form II instars.