A Successful Crayfish Invader Is Capable of Facultative Parthenogenesis: A Novel Reproductive Mode in Decapod Crustaceans

Biological invasions are impacting biota worldwide, and explaining why some taxa tend to become invasive is of major scientific interest. North American crayfish species, particularly of the family Cambaridae, are prominent invaders in freshwaters, defying the “tens rule” which states that only a minority of species introduced to new regions become established, and only a minority of those become invasive and pests. So far, success of cambarid invaders has largely been attributed to rapid maturation, high reproductive output, aggressiveness, and tolerance to pollution. We provide experimental evidence that females of one cambarid species particularly widespread in Europe, the spiny-cheek crayfish Orconectes limosus, are capable of facultative parthenogenesis. Such reproductive mode has never before been recognized in decapods, the most diverse crustacean order. As shown by analysis of seven microsatellite loci, crayfish females kept physically separated from males produced genetically homogeneous offspring identical with maternal individuals; this suggests they reproduced by apomixis, unlike those females which mated with males and had a diverse offspring. Further research is needed to clarify what environmental conditions are necessary for a switch to parthenogenesis in O. limosus, and what role it plays in natural crayfish populations. However, if such reproductive plasticity is present in other cambarid crayfish species, it may contribute to the overwhelming invasive success of this group

Reproductive plasticity in freshwater invader: from long-term sperm storage to parthenogenesis.

Orconectes limosus, a North American crayfish species, is one of the most important aquatic invaders in European inland waters. Despite more than 120 years occurrence in Europe and intense research, there are still gaps in knowledge of its life history and ecology. Investigation into O. limosus invasive success requires identifying the mechanisms that enabled them to establish dense and widespread populations from small initial numbers without observable limitation by an introduction bottleneck. In part, O. limosus success may lie in its ability to reproduce by facultative parthenogenesis. Moreover, there are possible other mating scenarios, because of two mating seasons (autumn and spring) in O. limosus. This work investigated the effect of four reproductive scenarios (autumn mating only, spring mating only, autumn and spring mating, and without mating) on the reproductive success of O. limosus. Females successfully reproduced in all tested mating regimes using parthenogenesis as well as log term sperm storage. This reproductive plasticity likely facilitates the overwhelming success of O. limosus spread and establishment in new localities. It can explain the spread of O. limosus from the initial introduction of 90 specimens to most of continental Europe and Great Britain. These conclusions imply a serious threat, not only for autochthonous European astacofauna, but for other aquatic organisms as well as entire ecosystems

Adaptation to pelleted feed in pikeperch fingerlings: learning from the trainer fish over gradual adaptation from natural food

Pikeperch (Sander lucioperca) is commercially important as well as a valued culinary fish with potential for intensive culture. One of the basic problems in pikeperch culture in recirculating aquaculture systems is adapting early life stages to pelleted feed (PF). Our work compares four different ways of adapting 6-week-old pikeperch fingerlings (standard length, SL = 29.30 ± 2.14 mm; weight, W = 0.38 ± 0.08 g) to feeding on a commercial diet. The methods are designated, A – use of trainer fish (Vimba vimba; SL = 36.88 ± 3.28 mm; W = 0.77 ± 0.26 g) and direct application of PF; B – use of trainer fish and gradual addition of PF with natural food (natural feed (NF), chironomid larvae); C – direct application of PF only; D – gradual addition of PF with NF. The growth trial experiment (including adaptation to PF) lasted 14 days by which time all experimental groups were accepting PF. Pikeperch fingerlings in group A grew significantly faster and PF was more readily accepted compared to other groups (SL = 46.11 ± 4.09 mm; W = 1.44 ± 0.38 g; specific growth rate = 9.48 ± 0.83% day−1). Other characteristics observed (total weight increment, feed conversion ratio) also support the use of trainer fish and direct application of PF for pikeperch in their adaptation to intensive culture. It is also an illustration of applicable use of learning potential in fish which can be usable for other fish species

Economic value of constructed wetland (CW) use in a recirculating hatchery system compared to operation without CW with different numbers of eyed eggs as initial stock per production cycle (PC).

<p>The mean final weight of fingerlings is based on the calculated possible maximum final biomass in the hatchery system. The price of fingerling is based on real prices at the study site. The annual price of fingerlings assumes four production cycles (PC) per year.</p><p><b>*</b> Converted from real fingerling prices of trout farm at the study site.</p><p>Economic value of constructed wetland (CW) use in a recirculating hatchery system compared to operation without CW with different numbers of eyed eggs as initial stock per production cycle (PC).</p

Schematic of recirculating hatchery system with the integrated constructed wetland: 1—fish tanks, 2—biofiltration/sedimentation unit, 3—circulation pump, 4—retention tank, 5—fresh water inlet, 6—ball valve, 7—constructed wetland (with the detail of water flow through tanks).

<p>Four water sampling sites are labelled: IF—inlet to fish tanks, OF—outlet from fish tanks, OB—outlet from biofilter, ICW—inlet to constructed wetland, OCW—outlet from constructed wetland, OP—outflow pipes, CP—connecting pipes for subsurface flow.</p

Native European branchiobdellids on non-native crayfishes: Report from the Czech Republic

Invasive alien species present a global threat to biodiversity, particularly where pathogens and symbionts are involved. Non-native crayfish species can increase their impact on the host ecosystem through introductions of symbiotic fauna. Conversely, non-native crayfishes could serve as hosts for native epibionts, thus substituting for disappearing native crayfishes as well. Here we report the presence of native branchiobdellids on naturalized populations of non-native crayfish Orconectes limosus and Pacifastacus leniusculus living in sympatry with native Astacus astacus. The native crayfish species probably served as a source of Branchiobdella spp. for non-native crayfishes. Two species of Branchiobdella (B. parasita and B. pentadonta) were found on P. leniusculus while only B. parasita was found on O. limosus. The level of colonization of inspected specimens and species was also evaluated. The mean number of branchiobdellids found on P. leniusculus and O. limosus was 26.0±15.9, and 64.8±27.7, respectively. Orconectes limosus was more heavily colonized by Branchiobdella despite being significantly smaller than P. leniusculus. Non-native species were corroborated as suitable to host the native epibionts

Energy consumption (kWh), freshwater demand (m³), and labour (hr) per day during Phase 1 and Phase 2 of the production cycle and for the entire production cycle (PC) in the recirculating hatchery system with (CW) and without (X) use of integrated constructed wetland.

<p>Energy consumption (kWh), freshwater demand (m³), and labour (hr) per day during Phase 1 and Phase 2 of the production cycle and for the entire production cycle (PC) in the recirculating hatchery system with (CW) and without (X) use of integrated constructed wetland.</p

Example of multilocus genotypes of 5 spiny-cheek crayfish females reproduced by apomictic parthenogenesis (Group 4), and their offspring.

<p>Alleles are given as fragment sizes in base pairs. All analyzed juveniles of these females had multilocus genotypes identical to their mothers, so only three juvenile genotypes are shown.</p