Genetic diversity and population structure of the invasive alien red swamp crayfish

High genetic diversity is thought to characterize successful invasive species, as the potential to adapt to new environments is enhanced and inbreeding is reduced. The red swamp crayfish, Procambarus clarkii, native to northeastern Mexico and south-central USA was introduced to Nanjing, China from Japan in 1929. Little is known about the genetic diversity and population structure of this species in China. We examined the genetic diversity and population structure of six P. clarkii populations using nine polymorphic microsatellites. Among the six populations, Nanjing population showed the highest allele number, allele richness and gene diversity, which is consistent with records indicating Nanjing may be the first site of introduction. In all six populations, significant heterozygote deficit was observed, suggesting founder effects and non-random mating. Analysis of bottleneck under infinite allele model, stepwise mutation model and two-phased model of mutation revealed evidence of a recent bottleneck in all these populations. Pairwise genetic distance analysis, AMOVA and assignment tests demonstrated high genetic differentiation between populations. Pairwise genetic distance did not fit the pairwise geographic distance, suggesting that human mediated dispersal have played a role in the population expansion and genetic differentiation.     

Minimum viable population sizes and global extinction risk are unrelated

Theoretical and empirical work has shown that once reduced in size and geographical range, species face a considerably elevated risk of extinction. We predict minimum viable population sizes (MVP) for 1198 species based on long-term time-series data and model-averaged population dynamics simulations. The median MVP estimate was 1377 individuals (90% probability of persistence over 100 years) but the overall distribution was wide and strongly positively skewed. Factors commonly cited as correlating with extinction risk failed to predict MVP but were able to predict successfully the probability of World Conservation Union Listing. MVPs were most strongly related to local environmental variation rather than a species' intrinsic ecological and life history attributes. Further, the large variation in MVP across species is unrelated to (or at least dwarfed by) the anthropogenic threats that drive the global biodiversity crisis by causing once-abundant species to decline.     

Intensive trapping and increased fish predation cause massive population decline of an invasive crayfish

1. Invasive species frequently have adverse impacts on native communities and ecosystems. Management options are often limited. Our goal is to evaluate the effect of intensive trapping and fish predation on the population dynamics of an invasive crayfish. 2. From 2001 to 2005, we removed invasive rusty crayfish (Orconectes rusticus) by trapping in Sparkling Lake in northern WI. In addition, the Wisconsin Department of Natural Resources restricted harvest of fish species known to consume crayfish, thereby increasing predation on crayfish that are too small to trap. 3. After an initial increase, catch rates of rusty crayfish declined by approximately 95%, from 11 crayfish per trap per day in 2002 to 0.65 in 2004. The catch rate in 2005 remained low at 0.5 crayfish per trap. Females comprised nearly 50% of the catch from 2002 to 2004. Unlike rusty crayfish in Sparkling Lake, catch rates of O. rusticus and Orconectes propinquus in three nearby lakes increased or remained relatively constant over the 5‐year removal period. 4. We also examined the influence of habitat and temperature on crayfish catch rates. Catch rates were highest at water temperatures between 20 and 25 °C and on cobble, log or macrophyte habitats that may serve as refuge from fish predation. 5. Five summers of intensive trapping and fisheries management practices reduced abundances, but did not extirpate rusty crayfish in Sparkling Lake. To determine the potential of trapping as a management option for invasive crayfishes, these methods must be tested in other systems.     

Dominance and diet selection in juncos

We measured the effects of dominance on diet in an aviary flockof seven dark-eyed juncos (Junco hyemalis).Preferences amongsix types of foods were recorded for each individual while solitary,and compared to that individual's diet when in the flock. Individualsspecialized on different foods during the flock trial. Subordinatesshowed greater shifts in diet between the solitary and flocktrials, had less diverse diets than dominants in the flock,and reduced the proportion of their diet consisting of preferredfoods to a greater extent than dominants. We interpret thischange in diet by subordinates as a response to interferencecompetition by dominants at preferred foods.     

An invasive crayfish affects egg survival and the potential recovery of an endangered population of Arctic charr

1. Many fish stocks have declined, because of overharvesting, habitat destruction and introduced species. Despite efforts to rehabilitate some of these stocks, not all are responding or are recovering only slowly. 2. In freshwater systems, introduced crayfish are often problematic, and it has been suggested that their egg predation could reduce recruitment in depleted stocks of native fish. 3. Here, we report the results of a field experiment, using experimental cages, on the extent of predation on eggs of great Arctic charr (Salvelinus umbla) in Lake Vättern, Europe’s fifth largest lake. Here, the great Arctic charr has declined dramatically and is listed as critically endangered. 4. We were able to partition the total loss rate of eggs into background mortality, predation by introduced signal crayfish (Pacifastacus leniusculus) and predation by native fish. The mortality rate of charr eggs because of crayfish was estimated at more than five times that because of native fish. Of the total loss of eggs, 80% is believed to be caused by crayfish and 14% by fish, with 6% being natural background mortality. 5. In a worst case scenario, our data infer that only 25% of the original number of eggs would survive, compared with 75% in the absence of crayfish. This could impair recovery of the stock of the endangered great Arctic charr in Lake Vättern. 6. Contrary to earlier claims that crayfish predation on eggs of great Arctic charr is insignificant, our results indicate that crayfish predation may exceed fish predation and suggest that the abundance of signal crayfish on the spawning sites of great Arctic charr should be managed.     

Effects of an invasive crayfish on the littoral macroinvertebrates of large boreal lakes are habitat specific

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Invasive zebra mussel colonisation of invasive crayfish: a case study

We investigated the interaction between two invasive invertebrate species in a shallow Central European flooded sandpit: the epibiosis of Ponto-Caspian zebra mussels Dreissena polymorpha on the American crayfish Orconectes limosus. Between 2004 and 2005, we followed the seasonal variation in number and size of the mussels attached to crayfish bodies, and microhabitats preferred by mussels. The proportion of crayfish colonised by mussels varied seasonally: in spring and early summer it was consistently over 75%, afterwards it dropped temporarily due to loss of bivalves during the crayfish moult, and later increased again due to re-colonisation by often relatively large juvenile mussels. Three different pathways of mussel settlement on crayfish hosts are likely: (1) primary settlement of free-swimming pediveliger larvae; (2) secondary settlement of plantigrade mussels and juveniles; (3) active re-attachment of grown mussels from the substrate to crayfish. This epibiosis was promoted by lack of suitable substrates at the studied locality. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Insight into invasion: Interactions between a critically endangered and invasive crayfish

Invasive species are known to competitively displace native species via direct behavioural interactions, or contests, which can result in limited access to valuable resources such as food or shelter for the native. Here, we aimed to determine the dynamics and outcome of agonistic contests between the critically endangered Fitzroy Falls Spiny Crayfish (Euastacus dharawalus) and the invasive yabby (Cherax destructor) in a controlled laboratory setting. Although C. destructor has been listed as a key threatening process for E. dharawalus, the magnitude and nature of its impact have not been formerly assessed. We recorded the frequency and intensity of aggressive interactions between the species, as well as the winner of the contest and subsequent dominance during staged encounters. In addition to this, we recorded the time individuals spent consuming food and actively moving on the substratum. Contrary to our predictions, the frequency of aggressive behaviours performed by the two species did not significantly differ, but E. dharawalus engaged in more intensely aggressive behaviours and was less submissive than C. destructor. As a result, E. dharawalus won significantly more contests than its invasive rival and subsequently achieved a higher dominance score overall. Despite this result, C. destructor spent significantly more time consuming food than did E. dharawalus. These results suggest that dominance in agonistic contests did not translate into dominance over food resources in our study. Ultimately, reduced access to food, combined with the costs of agonistic contests including injury and the relatively low reproductive rates of E. dharawalus indicate that C. destructor may have a negative effect on the survival and persistence of the critically endangered E. dharawalus.     

Native European eels as a potential biological control for invasive crayfish

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Behavioural determinants of agonistic success in invasive crayfish

Ecosystems today increasingly suffer invasions by multiple invasive species, some of which may share similar advantageous life history traits and ecological niche. In such cases, direct competition can influence invasion success of both species, and provide insights into competition without co-evolution in species equally novel to the environment. We used two widespread crayfish invaders of freshwater ecosystems of Europe, signal crayfish (Pacifastacus leniusculus) and spiny cheek crayfish (Orconectes limosus), to investigate how behavioural decisions in agonistic encounters contribute to competitive advantages in the absence of adaptation to either opponents or an environment. In direct competition against novel but comparable opponents, the key factor for establishing clear dominance of P. leniusculus in interspecific bouts was its greater tendency towards continued engagement in high-intensity fights. With O. limosus individuals consistently retreating from staged bouts as fights became more intense, P. leniusculus individuals did not need to adapt their strategy to be successful, suggesting that their agonistic behaviour intrinsically predisposed them to win. While both species are detrimental to invaded ecosystems, our results indicate that aggressive behaviour of P. leniusculus against unfamiliar opponents could allow it to more easily outcompete other comparable species and consequently present a potentially greater threat for native ecosystems.     

Dominance of a clonal green sulfur bacterial population in a stratified lake

For many years, the chemocline of the meromictic Lake Cadagno, Switzerland, was dominated by purple sulfur bacteria. However, following a major community shift in recent years, green sulfur bacteria (GSB) have come to dominate. We investigated this community by performing microbial diversity surveys using FISH cell counting and population multilocus sequence typing [clone library sequence analysis of the small subunit (SSU) rRNA locus and two loci involved in photosynthesis in GSB: fmoA and csmCA ]. All bacterial populations clearly stratified according to water column chemistry. The GSB population peaked in the chemocline ( c . 8 × 10⁶ GSB cells mL⁻¹) and constituted about 50% of all cells in the anoxic zones of the water column. At least 99.5% of these GSB cells had SSU rRNA, fmoA , and csmCA sequences essentially identical to that of the previously isolated and genome-sequenced GSB Chlorobium clathratiforme strain BU-1 (DSM 5477). This ribotype was not detected in Lake Cadagno before the bloom of GSB. These observations suggest that the C. clathratiforme population that has stabilized in Lake Cadagno is clonal. We speculate that such a clonal bloom could be caused by environmental disturbance, mutational adaptation, or invasion.     

Competition for shelter occupancy between a native freshwater crab and an invasive crayfish

Aquatic Ecology - Potamon potamios populations have decreased significantly due to the degradation of its habitat caused by human activities, mainly the use of insecticides. Today, P. potamios is...     

Behavioural and growth differences between experienced and naïve populations of a native crayfish in the presence of invasive rusty crayfish

1. Species invasions are a leading threat to native species and ecosystems. How populations of native species respond to the presence of invasive species will ultimately determine their long-term persistence.
2. In this study, we capitalise on a unique opportunity to compare the behaviour and growth of naïve and experienced virile crayfish ( Orconectes virilis Hagen) populations in the presence of invasive rusty crayfish ( O. rusticus Girard ) . In behavioural trials, experienced O. virilis (coexisted with O. rusticus for >30 years) showed more aggressive behaviour than their naïve counterparts. Naïve O . virilis retreated from aggressive interactions with O. rusticus 38% more often than experienced O . virilis. Experienced O. virilis spent 39% more time occupying shelter than naïve O. virilis.
3. There were also differences in O. rusticus behaviour: O. rusticus spent 24% more time occupying shelter with naïve O. virilis relative to experienced O. virilis .
4. In field mesocosm experiments with O. rusticus , naïve O . virilis declined in body mass by 1% while experienced O. virilis' body mass increased by 6%, thus highlighting the potential population-level implications of the previously observed behavioural effects.
5. Our work demonstrates significant behaviour and growth differences between naïve and experienced O. virilis in the presence of invasive O. rusticus. Whether this difference is the result of phenotypic plasticity or evolution by natural selection remains to be determined. Either way, this area of inquiry has implications for managing native populations and species in an increasingly invaded world.     

Divergent temperature-specific metabolic and feeding rates of native and invasive crayfish

Biological Invasions - Temperature is one of the most important factors governing the activity of ectothermic species, and it plays an important but less studied role in the manifestation of...     

Dominance of an invasive earthworm in native and non-native grassland ecosystems

More attention is currently being focused on earthworm invasions; however, in many ecosystems the relative abundance of native and invasive earthworm species is unknown. We characterized earthworm populations of two grassland types within the Palouse region: native prairie remnants and Conservation Reserve Program (CRP) set asides planted with exotic grasses. The earthworm community in both grassland types was completely dominated by the exotic-invasive Aporrectodea trapezoides. Only one individual of a native species, Driloleirus americanus (the giant Palouse earthworm), was found in a prairie remnant. No differences were found between prairie remnants and CRP sites for mean earthworm density (24–106 individuals m⁻²) or fresh weight (12–45 g m⁻²). Our results suggest that the combined effects of land-use change, habitat fragmentation and competitive interactions have resulted in the decimation of native earthworm populations and dominance of invasive earthworms in native and non-native grasslands of the Palouse region.     

Tests of Bacterial Strain Dominance within a Mouse Based on Sampling Faecal Colonies

This paper deals with making inferences about the dominance of a bacterial strain in a mouse gut based on strain typing of a random sample of colonies derived from plated faecal material.     

Managing invasive crayfish: use of X-ray sterilisation of males

1. In the last decade, many attempts have been made to contain the spread of the North American crayfish Procambarus clarkii , an invader of many European water bodies, but none has been successful.
2. This study investigates the effects that ionising irradiation has on the reproduction of P. clarkii males by analysing the behaviour of the treated individuals, their reproductive output, the vitality and survival of their offspring and the damages induced to their gonads.
3. We found that a dose of 20 Gy X-rays did not compromise either the survival or the mating ability of males, but reduced the size of their testes and significantly altered spermatogenesis. The number of aborted eggs was larger in clutches sired by treated males, with a consequent reduction (by 43%) in the number of offspring.
4. These results foster hopes in our efforts to control invasive crayfish, showing the potential effectiveness of ionising irradiation to reduce male fertility in the perspective of adopting the Sterile Male Release Technique to control P. clarkii populations.     

Trophic niches of three sympatric invasive crayfish of EU concern

The spread of non-native species results in novel and often unexpected assemblages. Using stable isotopes, we disentangled the trophic relationships between three invasive crayfish species at two sites of a small thermal tributary of the Barát stream, Hungary. We studied Procambarus virginalis and Faxonius limosus living in sympatry in the upper section of this thermal tributary, and then an assemblage in a lower section also containing P. clarkii. The two species in the upper section largely shared trophic niches, although P. virginalis was more carnivorous than F. limosus, which fed more on detritus and aquatic plants. In the lower section, P. clarkii had a distinctive trophic niche, being more carnivorous than the other species and also preying on other crayfish and fish. The trophic niches of the other two species shifted slightly, being narrower and more overlapping in the presence of P. clarkii. It seems that the presence of P. clarkii affects the feeding habits and trophic niches of the other two crayfish. Our results also indicate that the species have somewhat distinctive feeding niches, which suggests that the ecosystem effects of these species are likely to be at least partially additive in the shared localities.