Pietro Angelo Nardi

Female freshwater crayfish adjust egg and clutch size in relation to multiple male traits

Females may invest more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred partners may be fitter than offspring sired by non-preferred ones. In this study, we tested the differential maternal allocation hypothesis in the freshwater crayfish, Austropotamobius italicus, by means of a pairing experiment aimed at evaluating the effects of specific male traits (body size, chelae size and chelae asymmetry) on female primary reproductive effort. Our results showed that females laid larger but fewer eggs for relatively small-sized, large-clawed males, and smaller but more numerous eggs for relatively large-sized, small-clawed males. Chelae asymmetry had no effects on female reproductive investment. While the ultimate consequences of this pattern of female allocation remain unclear, females were nevertheless able to adjust their primary reproductive effort in relation to mate characteristics in a species where inter-male competition and sexual coercion may mask or obscure their sexual preferences. In addition, our results suggest that female allocation may differentially affect male characters, thus promoting a trade-off between the expression of different male traits.

Effects of female mating status on copulation behaviour and sperm expenditure in the freshwater crayfish Austropotamobius italicus

Sperm competition models predict that males should adjust their sperm expenditure according to the risk and/or intensity of sperm competition. In this paper, we analysed copulatory behaviour of both sexes and sperm expenditure in relation to female mating status (virgin or mated) in the freshwater crayfish Austropotamobius italicus, a species where males have been reported to feed on and remove sperm laid by other males. The same females were allowed to be inseminated sequentially by two males, and we compared the sexual behaviours of partners between the first (virgin females) and the second mating (mated females). We found that female resistance did not differ between the first and the second mating, nor males refused or took more time to mount a mated female. However, when mating with a mated female, males reached an effective copulation position significantly later. This occurred because second-mating males removed, by eating, all or most spermatophores previously deposited by first males. As removal was often incomplete, this resulted in a larger amount of sperm being deposited on female ventral parts after the second mating, although second males did not allocate more sperm to mated females than first males did. Thus, the peculiar mode of sperm competition, where males remove previously deposited sperm, and the consequent predictable strong last male prevalence in paternity likely led to the observed lack of adjustment of sperm expenditure to female mating status in this species.

Presence of rivals reduces mating probability but does not affect ejaculate size in the freshwater crayfish Austropotamobius italicus

Sperm competition models predict that males should adjust their sperm expenditure according to the risk and intensity of sperm competition, increasing it when competing with at least one other ejaculate and decreasing it when the number of competing ejaculates rises above two. However, when the raffle to fertilize eggs is strongly loaded due to sperm removal by subsequent rivals, it could be hypothesized that first-mating males progressively decrease their sperm expenditure and/or defer copulation with an increasing number of nearby competitors. Here, by varying experimentally the number of competitors around a mating pair, we analysed mating behaviour of both sexes and sperm expenditure in relation to variation in the immediate risk of sperm competition in the freshwater crayfish Austropotamobius italicus , a species where males remove all or part and feed on sperm laid by previous mating males. We found that male mating behaviour varied significantly with increasing number of rivals, because interactions between focal males and competitors, as well as male refusals to copulate, increased with number of the latter. As a consequence, the probability to reach an effective copulation decreased with increasing number of competitors. However, males released similar amounts of sperm independently of the number of surrounding competitors. Thus, the observed lack of variation in sperm expenditure in relation to the number of surrounding rivals suggests that freshwater crayfish males are unable to adjust the size of their ejaculates to short-term variation in the immediate risk of sperm competition.

Movement behaviour and shelter choice of the native crayfish Austropotamobius pallipes complex: survey on a population in a semi-natural pond in Northern Italy

This is a study of movements and artificial shelters use by a 3-year established population of Austropotamobius pallipes complex, in a lentic environment in the Parco Lombardo della Valle del Ticino (NW Italy). Home-checking and mark-recapture methods were used to investigate movements of 178 crayfish and shelter use by 389 crayfish in summer and in autumn. Most crayfish (97.2%) moved but the movement was highly variable. The greater part of the distances moved was less than 10 m day−1. Multi-hole bricks with one opening have been mostly selected, and the lower level was preferentially occupied; frequently a single crayfish per brick was found. The animals size affected the majority of the analysed variables: mean daily distance, area fidelity, level of shelter; on the other hand no case was significant for sex. The results highlight that this species is fairly mobile and could colonize waterbodies with similar features even rather rapidly. Mobility does not appear to affect the endangered status of this species.

Complexity of biogeographic pattern in the endangered crayfish Austropotamobius italicus in northern Italy: molecular insights of conservation concern

The protection of freshwater biodiversity has become a priority task for conservation practices, as freshwater ecosystems host high levels of cryptic diversity, while also record similarly high rates of extinction. The Italian white-clawed crayfish Austropotamobius italicus is an endemic freshwater crustacean, threatened by several anthropogenic impacts such as habitat fragmentation, pollution, invasion of exotics, and climate change. Previous phylogenetic studies conducted in Italy pointed out a complex phylogeographic framework for the species, with four different subspecies currently recognized. Conservation efforts, particularly when involving restocking and reintroduction, require a detailed knowledge of their population genetics. In this study we describe the genetic structure of A. italicus populations in northern Italy (Lombardy Alpine foothills and northern Apennines) by using the informative mitochondrial marker cytochrome c oxidase subunit I, in order to assess their current evolutionary diversity and past phylogeographic history from a conservation perspective. Our results contribute to the mapping of the contact area among A. i. carsicus and A. i. carinthiacus in the Orobie Larian Prealps. More interestingly, we highlight the existence of two deeply differentiated evolutionary lineages within A. i. carsicus, showing alternative phylogeographic patterns and past demographic trends. We propose to consider these two clades as distinct molecular operational taxonomic units for the conservation of this endangered crayfish.