Reproductive plasticity of a Procambarus clarkii population living 10°C below its thermal optimum

Abstract

In this study the annual reproductive biology of a Procambarus clarkii (Girard, 1852) population living in an atypical habitat with cold
\nspring waters is investigated by monitoring Gonado-Somatic and Hepato-Somatic Indexes (GSI and HSI) and by performing cytology on
\novaries. Despite its known preference for habitats with water temperature from 21 to 30 °C, our results clearly confirm the adaptation of this
\npopulation to the atypical thermal habitat, characterised by an annual mean water temperature value of 13.32 ±0.08 °C. Maximum gonadal
\ndevelopment was reached in August, with maximum GSI median value of 0.64 (instead of reported values even 10 times higher for other
\npopulations), and ovigerous females were found in autumn, with mean realized fecundity of 35 ±7 compared to 285–995 reported from other
\nhabitats. Histological analysis was consistent with other studies and allowed us to follow ovarian development at cytological level. The
\nimportance of all these results is not to be underestimated: to our knowledge these findings are the first report of the coolest habitat
\nsuccessfully colonized by this species at the present time and so they have to be taken as a warning about the possible range expansion of P.
\nclarkii also to northern and colder habitats that have few things in common with the native habitat of the species and, up to now, were
\nconsidered “safe” from the invasion of the red swamp crayfish.