Recent Invasive Species Research Articles

Differential influence of Pomphorhynchus laevis (Acanthocephala) on brain serotonergic activity in two congeneric host species.

The physiological mechanisms by which parasites with complex life cycles manipulate the behaviour of their intermediate hosts are still poorly understood. In Burgundy, eastern France, the acanthocephalan parasite Pomphorhynchus laevis inverses reaction to light in its amphipod host Gammarus pulex, but not in Gammarus roeseli, a recent invasive species. Here, we show that this difference in manipulation actually reflects a difference in the ability of the parasite to alter brain serotonergic (5-HT) activity of the two host species. Injection of 5-HT in uninfected individuals of both host species was sufficient to inverse reaction to light. However, a difference in brain 5-HT immunocytochemical staining levels between infected and uninfected individuals was observed only in G. pulex. Local adaptation of the parasite to the local host species might explain its inability to manipulate the behaviour and nervous system of the invasive species.

Leaf biomechanics as a potential tool to predict feeding preferences of the geometric tortoise Psammobates geometricus

Food and non food plant characteristics were studied for the geometric tortoise, Psammobates geometricus, to test the hypothesis that feeding preferences in tortoises may be influenced by the mechanical properties of plant leaves. Twelve focal feeding observations made between 8 October and 31 October 2002 were synthesized with literature reports to develop species lists of food and non food grasses and geophytes in renosterveld habitat. Failure load and tensile strength were determined in the field for leaves of food and non food plants that were spatially available to the tortoises and present in relative abundance during the course of the study. Leaves of geophyte food plants were fleshy and succulent with a low failure load and tensile strength. Leaves of food plant grasses had significantly higher failure loads and tensile strengths compared to leaves of food plant geophytes. In non food plants there was no signifi cant difference in failure load between grasses and geophytes, but tensile strength was signifi cantly higher in the grasses. Non food plant grasses and geophytes overall had significantly higher failure load and tensile strength values than did food plants. Two non food plants that overlapped in mechanical strength to the food plants either have toxic/unpalatable chemicals in high amounts or are recent invasive species to the renosterveld. Thus, these studies support the hypothesis that leaf biomechanical properties may be an important factor in determining the diet of the geometric tortoise and perhaps tortoises in general.

Reproductive success in male sunbleak, a recent invasive fish species in the U.K.

The spawning behaviour of male nest guarding sunbleak Leucaspius delineatus, a recent invasive species in southern England, was studied and quantified for the first time. In the absence of physical differences between territorial and non‐territorial males (i.e. colour, size, etc.), the reproductive behaviour of territorial males was analysed and related to reproductive success. The results showed that females preferred high‐courting and highly aggressive males. The initial cue in female mate choice, however, was based on courtship, while aggression was the decisive behavioural trait in influencing mate choice, providing a direct signal of physical condition and ‘paternal competence’. Some males picked nest sites which were subsequently preferred by other males taking over the nest of a previous male (‘communal nest’), with the new territorial male adopting the eggs already present at the nest. It appears that either due to female preference for nests already containing eggs or lower rates of sired egg predation by dilution among unrelated eggs, sunbleak males have adopted the mating strategy of allopaternal care.