Concomitant diel vertical migration of a predatory leech and its amphipod prey

SUMMARY.

• 1 The concomitant diet vertical migrations of the predaceous leech Erpobdella montezuma and its pelagic amphipod prey (Hyalella montezuma) were monitored for 1 year in Montezuma Well, Arizona, U.S.A.
• 2 High densities of H. montezuma occurred in the subsurface strata of the water column during the day, but a substantial portion of the population migrated into the surface 1 m at sunset. E. montezuma remained in the lower water strata during the day, but migrated vertically after sunset to exploit the high densities of H. montezuma near the surface. Densities of E. montezuma progressively increased in the upper strata of the water column after sunset as light energy fell below 1 μEin m^?2 s^?1.
• 3 It is suggested that the synchronized nocturnal migrations of the predator E. montezuma in relation to its prey H. montezuma, increases the foraging efficiency of the leech in the highly predictable environment of Montezuma Well.

     

Biogeographic comparisons of the traits and abundance of an invasive crab throughout its native and invasive ranges

High abundances of non-native species in the invaded range may be linked to changes in fitness related traits. However, few studies have compared differences in both life-history traits and abundances of introduced species between their native and invaded ranges. We determined differences in 12 morphological traits, an important fitness related trait (body size), and the abundance of the porcelain crab, Petrolisthes elongatus, in its native (New Zealand) and invasive (Tasmania, Australia) ranges. P. elongatus was more abundant in the introduced range; however, changes in abundance depended on tidal height, with higher abundances only at mid and low tidal zones. The biomass of male crabs was higher in the invaded range compared to the native range, but there was no difference in female biomass between ranges. Despite increases in male biomass, sex ratios between native and invasive populations did not differ. In addition, principal components analysis showed no differences in overall morphology between Tasmania and New Zealand. Our study indicates that increased abundance in the invaded range of P. elongatus may be linked to high values of an important trait (greater biomass) in the invaded range. Importantly, changes in biomass and abundance may be due to P. elongatus being able to utilise mid/low zones more in the invaded range. Furthermore, our findings indicate that understanding how sex specific changes in biomass interact with the recipient environment (biotic and abiotic) in the introduced range will be important for determining the mechanisms underpinning the establishment and spread of P. elongatus.     

Learning in an invasive and a native predatory crab

The invasion of the green crab Carcinus maenas in the northeastern U.S. and its competition with the native blue crab Callinectes sapidus and other native crustaceans has been well-documented and researched. Various reasons for the invader’s success against native crabs have been examined (juvenile predation, food source flexibility, etc.), but another possibility is a difference in the learning ability of invasive versus native crab species. In this study, the learning ability of C. maenas and C. sapidus was tested by their increased speed in locating hidden food over successive days. The data suggest that C. maenas possesses a learning ability significantly greater than that of C. sapidus, which may partially contribute to its success.     

Alfalfa fields promote high reproductive rate of an invasive predatory lady beetle

Invasive insect species often may attain high fecundity in agricultural habitats, thereby contributing to their establishment in new geographic regions and their displacement of similar native species. Such may be true for predatory lady beetles (Coleoptera: Coccinellidae) that have been introduced to North America in recent decades, raising concerns of adverse impact on native lady beetles. In northern Utah, Coccinella septempunctata L. first appeared in 1991, and is now predominant among lady beetles especially in alfalfa fields. We assessed the suitability of alfalfa fields as breeding habitat for females of C. septempunctata and the native, similarly sized Coccinella transversoguttata richardsoni Brown. The timing and amount of egg production differed significantly between C. septempunctata and C. transversoguttata as populations of aphids increased through spring and early summer. Reproduction by both species conformed to the egg window hypothesis, with populations of the predators producing most eggs before aphid numbers peaked. But consistently among fields and years, females of C. septempunctata produced more eggs, and did so earlier in the spring, than C. transversoguttata females even at low prey density. Furthermore, C. septempunctata females were more successful than females of C. transversoguttata in approaching their maximum body weights and reproductive output as measured in the laboratory under ideal conditions. The strong reproductive success of C. septempunctata may contribute to its displacement of C. transversoguttata in irrigated alfalfa in the generally arid Intermountain West of North America and to its establishment as an abundant species in this region of North America.     

Non-lethal effects of an invasive species in the marine environment: the importance of early life-history stages

Studies examining the effects of invasive species have focussed traditionally on the direct/lethal effects of the invasive on the native community but there is a growing recognition that invasive species may also have non-lethal effects. In terrestrial systems, non-lethal effects of invasive species can disrupt early life-history phases (such as fertilisation, dispersal and subsequent establishment) of native species, but in the marine environment most studies focus on adult rather than early life-history stages. Here, we examine the potential for an introduced sessile marine invertebrate (Styela plicata) to exert both lethal and non-lethal effects on a native species (Microcosmus squamiger) across multiple early life-history stages. We determined whether sperm from the invasive species interfered with the fertilisation of eggs from the native species and found no effect. However, we did find strong effects of the invasive species on the post-fertilisation performance of the native species. The invasive species inhibited the settlement of native larvae and, in the field, the presence of the invasive species was associated with a ten-fold increase in the post-settlement mortality of the native species, as well as an initial reduction of growth in the native. Our results suggest that larvae of the native species avoid settling near the invasive species due to reduced post-settlement survival in its presence. Overall, we found that invasive species can have complex and pervasive effects (both lethal and non-lethal) across the early life-history stages of the native species, which are likely to result in its displacement and to facilitate further invasion.     

Natural killers and biogenic amines: the paracrine regulation in the immune system

Natural killers are referred to the category of cells well known for their assistance in cyto-differentiation control. Mechanisms of such assistance include cytolytic and secretory effects on the target. In this aspect, the NK capacity to assist in local aminoregulatory processes by adrenalin, serotonin, histamine release contained in these cells granules is considered to be the least studied and the most problematic issue. The solution of this problem demands taking into consideration a number of conditions: the NK ability to receipt biogenic amines and peculiarities of receptor structure; principal differences in mechanism of action of biogenic amines which enter the cell through exogenous pathway or which are synthesized endogenously; correlation between biogenic amines presence in the granules and functional NK state. Hypothesis of generation connected with the problem suggests the NK assistance in cytolysis in concomitant mechanisms of paracrine regulation of cellular microenvironmental proliferative response, induction of local inflammatory and immunomodulating processes.     

Environmental tolerances of an invasive terrestrial amphipod, Arcitalitrus dorrieni (Hunt) in Britain

We investigated key physiological tolerances of the invasive euterrestrial talitrid amphipod (or landhopper) Arcitalitrus dorrieni; desiccation, salt, high and low temperatures. The critical relative humidity below which, A. dorrieni experiences desiccation stress is very high (95-100%), making it completely reliant on the leaflitter/soil microhabitat. It is tolerant of a wide range of (sea) salt concentrations (5-750 mOsmol l(-1)) but is extremely vulnerable below 5 mOsmol l(-1). A. dorrieni does not tolerate low temperatures with a mean lower limit of 1.4 degrees C, but with no individual surviving <0 degrees C. The range of upper thermal tolerance (30-37.3 degrees C) was similar to that found for other landhopper and beachflea species. Based on its tolerance to these environmental factors it is suggested that A. dorrieni has a limited potential to invade further into Britain, being restricted to areas with sufficiently high ion concentrations and mild winters.     

Natural killers in pregnancy: the problem of heterogeneity and the regulation of activity

Natural killer activity of pregnant women's peripheral blood lymphocytes and of cord blood was investigated. 3H-uridine labeled K-562 and human embryo fibroblasts (HEF) were used as target cells in cytotoxic test. The results of competitive inhibition test led us to a conclusion about the presence of some common K-562 and HEF surface structures recognized by NK cells. It was shown that the decline of NK activity of pregnant women and a low NK activity of cord blood were not associated with the influence of T-lymphocytes or adherent cells.     

Lack of anti-predator recognition in a marine isopod under the threat of an invasive predatory crab

Biological Invasions - The prey naïveté hypothesis suggests that the failure of prey to recognize novel predators as a threat is caused by a lack of anti-predator adaptations. We tested...     

FTO is expressed in neurones throughout the brain and its expression is unaltered by fasting

Single-nucleotide polymorphisms in the first intron of the ubiquitously expressed FTO gene are associated with obesity. Although the physiological functions of FTO remain unclear, food intake is often altered when Fto expression levels are manipulated. Furthermore, deletion of FTO from neurones alone has a similar effect on food intake to deletion of FTO in all tissues. These results indicate that FTO expression in the brain is particularly important. Considerable focus has been placed on the dynamic regulation of Fto mRNA expression in the hypothalamus after short-term (16-48 hour) fasting, but results have been controversial. There are no studies that quantify FTO protein levels across the brain, and assess its alteration following short-term fasting. Using immunohistochemistry, we found that FTO protein is widely expressed in mouse brain, and present in the majority of neurones. Using quantitative Western blotting and RT-qPCR we show that FTO protein and mRNA levels in the hypothalamus, cerebellum and rostral brain are relatively uniform, and levels in the brain are higher than in skeletal muscles of the lower limbs. Fasting for 18 hours does not alter the expression pattern, or levels, of FTO protein and mRNA. We further show that the majority of POMC neurones, which are critically involved in food intake regulation, also express FTO, but that the percentage of FTO-positive POMC neurones is not altered by fasting. In summary, we find no evidence that Fto/FTO expression is regulated by short-term (18-hour) fasting. Thus, it is unlikely that the hunger and increased post-fasting food intake caused by such food deprivation is driven by alterations in Fto/FTO expression. The widespread expression of FTO in neurones also suggests that physiological studies of this protein should not be limited to the hypothalamus.     

Reproductive traits of a nonindigenous amphipod associated with alternative habitat structures in presence of an invasive ecosystem-engineering polychaete

Hydrobiologia - Understanding reproductive traits of invasive species and their modulation by different invaded habitats is crucial for monitoring invasive processes. The invasive ecosystem...     

Chemoreception in an arctic amphipod crustacean: A field study

Traps baited with meat or fish were set through the ice in 5 m of water near Prudhoe Bay, Alaska. They were monitored by divers and surface observers. Over 99% of the animals attracted to the bait were the lysianassid amphipod Boeckosimus (= Onisimus) affinis (Hansen). Up to 20000 individuals were collected during each 24-h trapping period. Animals moved to the trap only from a downcurrent direction, and from a distance of up to at least 30 m away. It is suggested that chemoreception is the method used to find bait: animals swam into the current after receiving the stimulus and required a constant presence of stimulus at some threshold level to continue moving to the bait.     

Gradients of life-history variation: an intercontinental comparison of fishes

Multivariate analysis identified atwo-dimensional continuum of life-historyvariation among 301 fish species from Europe,North America, South America and the Atlanticand Pacific coasts of North America. The firstaxis was associated with larger body size,higher fecundity, delayed maturation, fewerreproductive events, and shorter breedingseason on one end and small size, lowfecundity, early maturity, multiplereproductive events per year, and prolongedbreeding season on the other. The second axiscontrasted fishes having larger eggs and moreparental care against fishes with the oppositesuite of traits.Phylogenetic affiliations of species wereapparent in the general patterns of ordinationof species within orders, indicatingevolutionary divergences in life-historypatterns. In fact, partitioning the variance oflife-history traits showed that taxonomic orderand latitude were the most important factorsand geographic region and habitat the least.Despite phylogenetic constraints, basiclife-history patterns showed consistencybetween distantly geographical regions,latitudinal ranges and basic adult habitats,indicating convergences in life-historypatterns. Although the basic life-historypatterns seemed repeatable among distantlyrelated taxa, geographical and latitudinalaffiliations were apparent. Species from SouthAmerica are skewed toward the opportunisticendpoint, whereas North American marine speciesare skewed toward the periodic endpoint of thetrilateral continuum model. Most of the fishspecies from South American data set came fromfluctuating environments, so an opportunisticstrategy of early maturation and continuousspawning permits efficient recolonization ofhabitats over small spatial scales. Incontrast, most species in the North Americanand European data sets came from seasonalhabitats that are nonetheless more hydrologicalstable, so a periodic strategy of delayingmaturation to attain large clutches enhancesadult survivorship during suboptimalenvironmental conditions and recruitment whenearly life stages encounter suitableenvironmental conditions. Similarly,latitudinal affiliations were also observed:opportunistic strategists more common intropical latitudes and periodic strategistsmore common in temperate and Arctic latitudes.