A behavioral syndrome linking boldness and flexibility facilitates invasion success in sticklebacks

ABSTRACTFor a species to expand its range, it needs to be good at dispersing and also capable of exploiting resources and adapting to different environments. Therefore, behavioral and cognitive traits could play key roles in facilitating invasion success. Here, we show that dispersing sticklebacks are bold, while sticklebacks that have recently established in a new region are flexible. Moreover, boldness and flexibility are negatively correlated with one another at the individual, family and population levels. Multiple lines of evidence suggest that the divergence in boldness and flexibility is likely to be evolutionary in origin. If boldness is favored in invaders during the initial dispersal stage, while flexibility is favored in recent immigrants during the establishment stage, then the link between boldness and flexibility could generate positive correlations between successes during both dispersal and establishment, and therefore play a key role in facilitating colonization success in sticklebacks and other organisms.

Microbial Grazers May Aid in Controlling Infections Caused by the Aquatic Zoosporic Fungus Batrachochytrium dendrobatidis

Free-living eukaryotic microbes may reduce animal diseases. We evaluated the dynamics by which micrograzers (primarily protozoa) apply top-down control on the chytrid Batrachochytrium dendrobatidis (Bd) a devastating, panzootic pathogen of amphibians. Although micrograzers consumed zoospores (∼3 μm), the dispersal stage of chytrids, not all species grew monoxenically on zoospores. However, the ubiquitous ciliate Tetrahymena pyriformis, which likely co-occurs with Bd, grew at near its maximum rate (r = 1.7 d–1). A functional response (ingestion vs. prey abundance) for T. pyriformis, measured using spore-surrogates (microspheres) revealed maximum ingestion (Imax) of 1.63 × 103 zoospores d–1, with a half saturation constant (k) of 5.75 × 103 zoospores ml–1. Using these growth and grazing data we developed and assessed a population model that incorporated chytrid-host and micrograzer dynamics. Simulations using our data and realistic parameters obtained from the literature suggested that micrograzers could control Bd and potentially prevent chytridiomycosis (defined as 104 sporangia host–1). However, simulated inferior micrograzers (0.7 × Imax and 1.5 × k) did not prevent chytridiomycosis, although they ultimately reduced pathogen abundance to below levels resulting in disease. These findings indicate how micrograzer responses can be applied when modeling disease dynamics for Bd and other zoosporic fungi.

Larval energetics of the Sydney rock oyster Saccostrea glomerata and Pacific oyster Magallana gigas

Larvae are a critical dispersal stage of marine invertebrates, and their survival depends on nutrition and energetics. This study compared the size, survival, metabolic rate and egg and larval lipid class profiles of larvae of the endemic Sydney rock oyster Saccostrea glomerata and the invasive Pacific oyster Magallana gigas through a period of starvation for 5 and 9 d after fertilisation. Starved larvae grew without food until 5 d of age, at which point they stopped developing, but resumed growth when fed. Egg lipids profiles comprised 78.1 and 74.5% triacylglycerol for M. gigas and S. glomerata respectively. When fed, larvae of M. gigas were significantly larger in size and had faster growth and similar survival compared to S. glomerata. When starved, larvae of M. gigas and S. glomerata grew at similar rates, and there was a trend for lower survival of M. gigas. Larval endogenous lipid reserves were deleted in the first 24 h. Larvae of M. gigas had more total lipids and comparatively more diacylglycerols, monoacylglycerols, phospholipids and cholesterol, whereas S. glomerata had more diacylglycerols and produced sterol esters. Starvation altered the patterns of lipid assimilation, and metabolic rates of larvae of M. gigas and S. glomerata differed over time. When starved, S. glomerata larvae had greater capacity to cope with starvation compared to M. gigas, perhaps due to an evolutionary history in oligotrophic estuaries. As the climate rapidly changes in this global climate-change hotspot, S. glomerata is likely to be negatively affected.

Microbial grazers may aid in controlling infections caused by aquatic zoosporic fungi

Free-living eukaryotic microbes may reduce animal diseases. We evaluated the dynamics by which micrograzers (primarily protozoa) apply top-down control on the chytrid Batrachochytrium dendrobatidis (Bd) a devastating, panzootic pathogen of amphibians. Although micrograzers consumed zoospores (∼3 µm), the dispersal stage of chytrids, not all species grew monoxenically on zoospores. However, the ubiquitous ciliate Tetrahymena pyriformis, which likely co-occurs with Bd, grew at near its maximum rate (r = 1.7 d-1). A functional response (ingestion vs. prey abundance) for T. pyriformis, measured using spore-surrogates (microspheres) revealed maximum ingestion (Imax) of 1.63 × 103 zoospores d-1, with a half saturation constant (k) of 5.75 × 103 zoospores ml-1. Using these growth and grazing data we developed and assessed a population model that incorporated chytrid-host and micrograzer dynamics. Simulations using our data and realistic parameters obtained from the literature suggested that micrograzers could control Bd and potentially prevent chytridiomycosis (defined as 104 sporangia host-1). However, simulated inferior micrograzers (0.7 x Imax and 1.5 x k) did not prevent chytridiomycosis, although they ultimately reduced pathogen abundance to below levels resulting in disease. These findings indicate how micrograzer responses can be applied when modelling disease dynamics for Bd and other zoosporic fungi.

Pine chemical volatiles promote dauer recovery of a pine parasitic nematode, Bursaphelenchus xylophilus

Pinewood nematode, Bursaphelenchus xylophilus, a pine parasitic nematode, poses a serious threat to its host pine forests globally. When dispersal-stage larvae 4 (dauer, DL4) of B. xylophilus enters the new pine, it moults into propagative adult (dauer recovery) and reproduces quickly to kill the host pine. Here, we found pine chemical volatiles, rather than the common dauer recovery factors of nematodes (e.g. suitable temperatures, nutrient availability or density), promote B. xylophilus dauer recovery. The results showed that volatilization of chemicals in host pines could attract DL4 and promote DL4 recovery. To identify which chemicals promote this process, we determined the stimulated activity of the main volatiles of pines including six monoterpenes and two sesquiterpenes. Results showed that all the six monoterpenes promoted dauer recovery, especially β-pinene and β-myrcene, but the two sesquiterpenes have no effect on the transformation. Furthermore, β-pinene performed gradient effects on dauer recovery. We hypothesized that when DL4 infect pine trees, the pine volatiles released from the feeding wounds are used as chemical signals for DL4 transformation to adult to reproduce and rapidly kill the pines. Our study identified the B. xylophilus dauer recovery chemical signal and may contribute to preventing pine wilt disease.

An explicit formula for a dispersal kernel in a patchy landscape

Integrodifference equations (IDEs) are often used for discrete-time continuous-space models in mathematical biology. The model includes two stages: the reproduction stage, and the dispersal stage. The output of the model is the population density of a species for the next generation across the landscape, given the current population density. Most previous models for dispersal in a heterogeneous landscape approximate the landscape by a set of homogeneous patches, and allow for different demographic and dispersal rates within each patch. Some work has been done designing and analyzing models which also include a patch preference at the boundaries, which is commonly referred to as the degree of bias. Individuals dispersing across a patchy landscape can detect the changes in habitat at a neighborhood of a patch boundary, and as a result, they might change the direction of their movement if they are approaching a bad patch.In our work, we derive a generalization of the classic Laplace kernel, which includes different dispersal rates in each patch as well as different degrees of bias at the patch boundaries. The simple Laplace kernel and the truncated Laplace kernel most often used in classical work appear as special cases of this general kernel. The form of this general kernel is the sum of two different terms: the classic truncated Laplace kernel within each patch, and a correction accounting for the bias at patch boundaries.

Effects of cell morphology and attachment to a surface on the hydrodynamic performance of unicellular choanoflagellates

Choanoflagellates, eukaryotes that are important predators on bacteria in aquatic ecosystems, are closely related to animals and are used as a model system to study the evolution of animals from protozoan ancestors. The choanoflagellate Salpingoeca rosetta has a complex life cycle with different morphotypes, some unicellular and some multicellular. Here we use computational fluid dynamics to study the hydrodynamics of swimming and feeding by different unicellular stages of S. rosetta : a swimming cell with a collar of prey-capturing microvilli surrounding a single flagellum, a thecate cell attached to a surface and a dispersal-stage cell with a slender body, long flagellum and short collar. We show that a longer flagellum increases swimming speed, longer microvilli reduce speed and cell shape only affects speed when the collar is very short. The flux of prey-carrying water into the collar capture zone is greater for swimming than sessile cells, but this advantage decreases with collar size. Stalk length has little effect on flux for sessile cells. We show that ignoring the collar, as earlier models have done, overestimates flux and greatly overestimates the benefit to feeding performance of swimming versus being attached, and of a longer stalk for attached cells.

Off-host longevity of the winged dispersal stage ofCarnus hemapterus(Insecta: Diptera) modulated by gender, body size and food provisioning

Highlighting the dispersal ecology of parasites is important for understanding epidemiological, demographic and coevolutionary aspects of host–parasite interactions. Yet, critical aspects of the dispersal stage of parasites, such as longevity and the factors influencing it, are poorly known. Here we study the lifespan of the dispersal stage of an ectoparasitic dipteran,Carnus hemapterus, and the impact of gender, body size and food provisioning on longevity. We found that freshly emerged imagoes survive at most less than 4 days. Longevity increased with body size and, since this parasite exhibits sexual size dimorphism, the bigger females lived longer than males. However, controlling for body size suggests that males lived relatively longer than females. Furthermore, a humid environment and food provisioning (flowers) significantly increased individual life spans. We discuss the relative importance of spatial and temporal dispersal in relation to the infectious potential of this parasite.

Pre- dispersal seed loss of Ramorinoa girolae (Fabaceae) in Ischigualasto Provincial Park (San Juan, Argentina

Ramorinoa girolae Speg. is a “vulnerable” tree endemic to Argentina. During the pre-dispersal stage, the seeds are predated by Anypsipyla univitella. The objectives of this study were to describe some reproductive parameters (size and number of fruits and seeds) of R. girolae, to quantify pre-dispersal seed loss by abortion and predation, and to test the effect on pre-dispersal seed predation of fruit production (per tree, of co-specific neighbors, and the sum of both), size of fruits, number of seeds per fruit, and number of predators per fruit. As seeds can be partially consumed by the predator, the viability of partially damaged seeds was assessed as well. At Ischigualasto Park, we sampled 17 adult trees from 3 stands spaced 4 km apart. For each focal tree, we quantified the number of co-specific neighbors and their fruits. We collected ten fruits from canopies and recorded their length and the number and states of seeds (intact, predated, and aborted). Generalized Linear Mixed Models were fitted to evaluate explanatory variables affecting the proportion of pre-dispersal predated seeds. R. girolae suffers great loss of seeds during the pre-dispersal stage, mainly by seed predation (58% of seeds). The proportion of predated seeds was most important relative to the number of predators, the number of seeds per fruit, and the size of fruits. Fruits containing more predators, more seeds, and smaller fruits had higher proportions of predated seeds. Seed abortion would not represent an important factor of seed loss (6% of seeds