Seeing a Ghost? Vigilance and Its Drivers in a Predator‐free World

Vigilance is a key to the early detection of predators, but may be costly if it impairs foraging efficiency. Hence, we would expect vigilance to be suppressed and/or counter‐selected in predator‐free environments, although this might depend on the environmental drivers influencing perceived predation risk. We studied vigilance in two populations of Sitka black‐tailed deer (Odocoileus hemionus sitkensis) on Haida Gwaii (Canada) which have not been exposed to predators since they colonized the study islands approx. 60 yr ago. In this context, anti‐predator behavior should not have any obvious current benefit. Moreover, its maintenance should be particularly costly in our study populations because these deer have depleted their food resources and, thus, anti‐predator behaviors should interfere with time spent searching for scarce resources. We used bait stations equipped with camera traps to assess vigilance under standardized feeding conditions. We expected to observe lower vigilance levels than those observed elsewhere in locations with predators. We investigated how vigilance varied in relation to the amount of bait, the level of visibility, and between day and night. During the day, deer spent, on average, 14% of their time in overt vigilance during foraging bouts, a level similar to, although in the lower range of, values reported at sites where predators are present. Levels of vigilance were lower at night, and decreased with increasing visibility, but not during the day. Deer were less vigilant when bait availability was high, but only when visibility was also high. We discuss why the maintenance of vigilance is here best explained by the ghosts of predators past, and how, at the temporal scale of a few generations, the ecological factors driving vigilance levels might override the absence of significant risk from large predators.     

Adaptive radiation in extremophilic Dorvilleidae (Annelida): diversification of a single colonizer or multiple independent lineages?

Metazoan inhabitants of extreme environments typically evolved from forms found in less extreme habitats. Understanding the prevalence with which animals move into and ultimately thrive in extreme environments is critical to elucidating how complex life adapts to extreme conditions. Methane seep sediments along the Oregon and California margins have low oxygen and very high hydrogen sulfide levels, rendering them inhospitable to many life forms. Nonetheless, several closely related lineages of dorvilleid annelids, including members of Ophryotrocha, Parougia, and Exallopus, thrive at these sites in association with bacterial mats and vesicomyid clam beds. These organisms are ideal for examining adaptive radiations in extreme environments. Did dorvilleid annelids invade these extreme environments once and then diversify? Alternatively, did multiple independent lineages adapt to seep conditions? To address these questions, we examined the evolutionary history of methane-seep dorvilleids using 16S and Cyt b genes in an ecological context. Our results indicate that dorvilleids invaded these extreme habitats at least four times, implying preadaptation to life at seeps. Additionally, we recovered considerably more dorvilleid diversity than is currently recognized. A total of 3 major clades (designated “Ophryotrocha,” “Mixed Genera” and “Parougia”) and 12 terminal lineages or species were encountered. Two of these lineages represented a known species, Parougia oregonensis, whereas the remaining 10 lineages were newly discovered species. Certain lineages exhibited affinity to geography, habitat, sediment depth, and/or diet, suggesting that dorvilleids at methane seeps radiated via specialization and resource partitioning.     

Do plant‐eating insect lineages pass through phases of host‐use generalism during speciation and host switching? Phylogenetic evidence

The Oscillation Hypothesis posits that plant‐eating insect diversity is generated by cycles of diet breadth expansion and contraction. Although at any given time most plant‐eating insect species are host specialists, host‐use evolution and speciation tend to entail a phase of generalism. The main evidence for this comes from comparative phylogenetic studies, but with mixed support. Here, I review and add to this evidence. I show that some of the original work that inspired the Oscillation Hypothesis is flawed in a way that leads to spurious inferences about trends in the evolution of diet diversity. And I present a new analysis which fails to support its predictions about patterns of species diversity. On the other hand, some of the published work that claims to reject the Oscillation Hypothesis may actually provide some of the strongest support for it, and I present new analyses which support its prediction that host‐use generalism facilitates host‐use evolution. In summary, the Oscillation Hypothesis successfully predicts some phylogenetic patterns but not others. Generalism appears to facilitate host‐use evolution, but it does not appear to be inevitably chased by host‐use specialization and speciation.     

The palatability of Neotropical poison frogs in predator‐prey systems: do alkaloids make the difference?

Neotropical poison frogs sequester alkaloid‐based chemical defenses from their diet, which seem to repel invertebrate predators after contact. In this study, we tested the reaction of predatory ants toward skin secretions of captive‐bred poison frogs without alkaloids. Although the secretions had a smell and taste similar to those of wild‐caught frogs, the ants did not avoid them, but actually preferred them. We infer that amphibian secretions are attractive to invertebrate predators (probably due to palatable nutritive components), but that this attraction is overridden when unpalatable alkaloids are present.     

Why does the magnitude of genotype‐by‐environment interaction vary?

Genotype‐by‐environment interaction (G × E), that is, genetic variation in phenotypic plasticity, is a central concept in ecology and evolutionary biology. G×E has wide‐ranging implications for trait development and for understanding how organisms will respond to environmental change. Although G × E has been extensively documented, its presence and magnitude vary dramatically across populations and traits. Despite this, we still know little about why G × E is so evident in some traits and populations, but minimal or absent in others. To encourage synthetic research in this area, we review diverse hypotheses for the underlying biological causes of variation in G × E. We extract common themes from these hypotheses to develop a more synthetic understanding of variation in G × E and suggest some important next steps.     

Do host species evolve a specific response to slave-making ants?

Background

Social parasitism is an important selective pressure for social insect species. It is particularly the case for the hosts of dulotic (so called slave-making) ants, which pillage the brood of host colonies to increase the worker force of their own colony. Such raids can have an important impact on the fitness of the host nest. An arms race which can lead to geographic variation in host defenses is thus expected between hosts and parasites. In this study we tested whether the presence of a social parasite (the dulotic ant Myrmoxenus ravouxi) within an ant community correlated with a specific behavioral defense strategy of local host or non-host populations of Temnothorax ants. Social recognition often leads to more or less pronounced agonistic interactions between non-nestmates ants. Here, we monitored agonistic behaviors to assess whether ants discriminate social parasites from other ants. It is now well-known that ants essentially rely on cuticular hydrocarbons to discriminate nestmates from aliens. If host species have evolved a specific recognition mechanism for their parasite, we hypothesize that the differences in behavioral responses would not be fully explained simply by quantitative dissimilarity in cuticular hydrocarbon profiles, but should also involve a qualitative response due to the detection of particular compounds. We scaled the behavioral results according to the quantitative chemical distance between host and parasite colonies to test this hypothesis.

Results

Cuticular hydrocarbon profiles were distinct between species, but host species did not show a clearly higher aggression rate towards the parasite than toward non-parasite intruders, unless the degree of response was scaled by the chemical distance between intruders and recipient colonies. By doing so, we show that workers of the host and of a non-host species in the parasitized site displayed more agonistic behaviors (bites and ejections) towards parasite than toward non-parasite intruders.

Conclusions

We used two different analyses of our behavioral data (standardized with the chemical distance between colonies or not) to test our hypothesis. Standardized data show behavioral differences which could indicate qualitative and specific parasite recognition. We finally stress the importance of considering the whole set of potentially interacting species to understand the coevolution between social parasites and their hosts.

     

Do spatial effects play a role in the spatial distribution of desert‐dwelling Acacia raddiana?

Abstract. We investigated the spatial pattern of A. raddiana in the Negev desert of Israel in order to gain insights into the factors and processes driving the dynamics of this species. Using a scale‐dependent measure, the ring statistic, we analysed both patterns observed in the field and time series of spatial tree distributions produced by a simulation model. In the field, random spacing was the predominant pattern observed. However seedlings were clumped on small scales. We ran the model under two contrasting scenarios representing hypotheses that explain the clumping of seedlings and the random distribution of trees. One hypothesis is that there is spatial heterogeneity in seed distribution, germination and seedling mortality, but that these heterogeneities are not correlated with each other in space. The second hypothesis assumes a correlation between these heterogeneities leading to areas suitable for establishment. However, the suitability of the sites is temporally variable. Furthermore, the second hypothesis assumes density‐dependent tree mortality due to competition. Both hypotheses lead to spatial distributions that are in qualitative agreement with the patterns observed in the field. Therefore, the classical view that a clumped seedling distribution and a random pattern of older trees is due to clumped regeneration and density‐dependent mortality may not hold for Acacia trees in the Negev.     

The hemolymph proteome of the honeybee: Gel‐based or gel‐free?

The honeybee has an invaluable economic impact and is a model for studying immunity, development and social behavior. The recent sequencing and annotation of the honeybee genome facilitates the study of its hemolymph, which reflects the physiological condition and mediates immune responses. We aimed at making a proteomic reference map of honeybee hemolymph and compared gel‐free and gel‐based techniques. One hundered and four 2‐DE spots corresponding to 62 different proteins were identified. Eight identical 2‐DLC experiments resulted in the identification of 32 unique proteins. One repeat was clearly not representative for the potential of the given 2‐DLC setup. Only 27% of the identified hemolymph proteins were found by both techniques. In addition, we found proteins of three different viruses which creates possibilities for biomarker design. Future hemolymph studies will benefit from this work.     

Do agricultural pollutants affect competition between filter‐feeding caddis fly larvae? Results of laboratory microcosm experiments

1. Predictable changes in the composition of macroinvertebrate communities in response to non‐point source pollution are the basis of macroinvertebrate community indices. However, other factors, such as biotic interactions, also affect the composition of macroinvertebrate communities and may complicate the interpretation of such indices by interacting with abiotic stressors. 2. The effect of agricultural pollutants on competition between two filter‐feeding caddisflies, Brachycentrus appalachia and Hydropsyche spp. was studied in the laboratory using recirculating flow tanks. 3. Experiments were conducted at two densities of Hydropsyche: high (300 per tank) and low (80 per tank). Brachycentrus density was kept constant at 40 per tank in all experiments. Experiments assessed the effect of an agricultural pollutant mix (sand, cow‐manure compost mix) and the presence of the competitor on both taxa. 4. The only negative response to pollutants was a larger number of Hydropsyche drifting in high‐density tanks. In fact, at high densities, mortality of Hydropsyche was higher in controls than in tanks receiving pollutants. 5. Hydropsyche and B. appalachia competed for resources and the presence of pollution did not affect the outcome of this competition. The presence of high densities of Hydropsyche resulted in higher drift and lower condition of B. appalachia. At low densities of Hydropsyche, B. appalachia larvae suffered greater mortality and tended to be in poorer condition. Brachycentrus appalachia may be less successful at even moderate densities of Hydropsyche due to competition between these taxa, most likely for prime feeding positions. 6. Streams receiving non‐point source pollution from agriculture may be able to support higher densities of Hydropsyche, which may further reduce the suitability of these habitats for B. appalachia. 7. This experimental study suggests that competition may complicate interpretation of biotic indices, as changes in benthic invertebrate community structure normally ascribed to pollution may arise from intra‐specific competition.     

Do phytoplankton communities evolve through a self-regulatory abundance–diversity relationship?

A small group of phytoplankton species that produce toxic or allelopathic chemicals has a significant effect on plankton dynamics in marine ecosystems. The species of non-toxic phytoplankton, which are large in number, are affected by the toxin-allelopathy of those species. By analysis of the abundance data of marine phytoplankton collected from the North-West coast of the Bay of Bengal, an empirical relationship between the abundance of the potential toxin-producing species and the species diversity of the non-toxic phytoplankton is formulated. A change-point analysis demonstrates that the diversity of non-toxic phytoplankton increases with the increase of toxic species up to a certain level. However, for a massive increase of the toxin-producing species the diversity of phytoplankton at species level reduces gradually. Following the results, a deterministic relationship between the abundance of toxic phytoplankton and the diversity of non-toxic phytoplankton is developed. The abundance-diversity relationship develops a unimodal pathway through which the abundance of toxic species regulates the diversity of phytoplankton. These results contribute to the current understanding of the coexistence and biodiversity of phytoplankton, the top-down vs. bottom-up debate, and to that of abundance-diversity relationship in marine ecosystems.     

Do trophic subsidies affect the outcome of introductions of a non‐native freshwater fish?

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Does high relatedness promote cheater‐free multicellularity in synthetic lifecycles?

The evolution of multicellularity is one of the key transitions in evolution and requires extreme levels of cooperation between cells. However, even when cells are genetically identical, noncooperative cheating mutants can arise that cause a breakdown in cooperation. How then, do multicellular organisms maintain cooperation between cells? A number of mechanisms that increase relatedness amongst cooperative cells have been implicated in the maintenance of cooperative multicellularity including single‐cell bottlenecks and kin recognition. In this study, we explore how relatively simple biological processes such as growth and dispersal can act to increase relatedness and promote multicellular cooperation. Using experimental populations of pseudo‐organisms, we found that manipulating growth and dispersal of clones of a social amoeba to create high levels of relatedness was sufficient to prevent the spread of cheating mutants. By contrast, cheaters were able to spread under low‐relatedness conditions. Most surprisingly, we saw the largest increase in cheating mutants under an experimental treatment that should create intermediate levels of relatedness. This is because one of the factors raising relatedness, structured growth, also causes high vulnerability to growth rate cheaters.     

Is foraging innovation lost following colonization of a less variable environment? A case study in surface‐ vs. cave‐dwelling Asellus aquaticus

Behavioral innovation is a key process for successful colonization of new habitat types. However, it is costly due to the necessary cognitive and neural demands and typically connected to ecological generalism. Therefore, loss of behavioral innovativeness is predicted following colonization of new, simple, and invariable environments. We tested this prediction by studying foraging innovativeness in the freshwater isopod Asellus aquaticus. We sampled its populations along the route of colonizing a thermokarstic water‐filled cave (simple, stable habitat with only bacterial mats as food) from surface habitats (variable environment, wide variety of food). The studied cave population separated from the surface populations at least 60,000 years ago. Animals were tested both with familiar and novel food types (cave food: bacterial mats; surface food: decaying leaves). Irrespective of food type, cave individuals were more likely to feed than surface individuals. Further, animals from all populations fed longer on leaves than on bacteria, even though leaves were novel for the cave animals. Our results support that cave A. aquaticus did not lose the ability to use the ancestral (surface) food type after adapting to a simple, stable, and highly specialized habitat.     

Do we similarly assess diversity with microscopy and high-throughput sequencing? Case of microalgae in lakes

Diatoms are a species-diverse phylum of microalgae often presenting high biomass in aquatic habitats. This makes them excellent ecological indicators in rivers and lakes. They are routinely used to assess ecological quality of rivers and lakes using microscopy, which is time consuming. An alternative is to determine species in samples based on short DNA barcodes and high-throughput sequencing (HTS). Former studies showed that community structure and water quality assessments based on diatoms deliver similar results with both methods. But, none evaluated if diversities were assessed in the same way despite the importance of this ecological metric. Based on littoral benthic samplings carried out in 56 pristine alpine lakes, we compared different diversity indices measured with microscopy and metabarcoding. Each lake was sampled in three different places of its littoral. We showed that α (diversity measured in a single sampling site of a given lake) and ? (total diversity in a lake where three independent samples were considered) diversities obtained with HTS were higher than those obtained with microscopy. This may be explained by the capacity of HTS to detect morphologically cryptic species and to better detect rare taxa. On the other hand, β diversity obtained with HTS was smaller, which may be explained by the capacity of HTS to detect very rare species and free-floating extracellular DNA. Nevertheless, diversity indices obtained with both methodologies were well correlated each other. This study validates the possibility to assess diatom diversity with HTS in a comparable way to the classical microscopic analysis.     

Retromer and the cation‐independent mannose 6‐phosphate receptor—Time for a trial separation?

The retromer cargo‐selective complex (CSC) comprising Vps35, Vps29 and Vps26 mediates the endosome‐to‐Golgi retrieval of the cation‐independent mannose 6‐phosphate receptor (CIMPR). Or does it? Recently published data have questioned the validity of this long‐established theory. Here, the evidence for and against a role for the retromer CSC in CIMPR endosome‐to‐Golgi retrieval is examined in the light of the new data that the SNX‐BAR dimer is actually responsible for CIMPR retrieval.