Prey DNA detection success following digestion by intraguild predators: influence of prey and predator species

Intraguild predation (IGP) has been increasingly recognized as an important interaction in ecological systems over the past two decades, and remarkable insights have been gained into its nature and prevalence. We have developed a technique using molecular gut-content analysis to compare the rate of IGP between closely related species of coccinellid beetles (lady beetles or ladybirds), which had been previously known to prey upon one another. We first developed PCR primers for each of four lady beetle species: Harmonia axyridis, Coccinella septempunctata, Coleomegilla maculata and Propylea quatuordecimpunctata. We next determined the prey DNA detection success over time (DS(50) ) for each combination of interacting species following a meal. We found that DS(50) values varied greatly between predator-prey combinations, ranging from 5.2 to 19.3 h. As a result, general patterns of detection times based upon predator or prey species alone are not discernable. We used the DS(50) values to correct field data to demonstrate the importance of compensation for detection times that are specific to particular predator-prey combinations.     

Retention, capture and consumption of experimental prey by orb-web weaving spiders in coffee plantations of Southern Mexico

This study focuses on the predatory capacity of four sympatric species of web- building spiders that inhabit coffee plantations in Southern Mexico: Gasteracantha cancriformis, Cyclosa caroli, and the morphologically similar species pair Leucauge mariana and L. venusta which were considered as one species group. The retention capabilities of the webs of these species and the incidence of prey capture and consumption were measured using eight types of insect prey belonging to the orders Coleoptera (1 species), Hymenoptera (3), Diptera (2) Lepidoptera (1) and Homoptera (1). The different characteristics of each prey such as body weight, body size, defensive behaviour, etc., were recorded. The incidence of prey retention, capture and consumption were significantly higher in G. cancriformis than in any of the other species. The lowest rates of retention, capture and consumption were observed in C. caroli, while L. mariana/venusta were intermediate in their predatory capabilities. Significant negative correlations between prey size and percent consumption were detected in L. mariana/venusta and in G. cancriformis; in both cases, large prey were less likely to be immediately consumed than small prey items. The results can be interpreted in the light of the morphological characteristics of the spiders. G. cancriformis possesses long legs and a carapace and appeared to have few difficulties to manipulate all types of prey. In contrast, C. caroli showed lesser abilities to manipulate and subdue aggressive prey items, perhaps due to the short leg length and unprotected body of this species. The consumption of prey items may be related to the predatory strategy of each spider. G. cancriformis constructs a new web every morning and prey storage was never observed. The absence of prey storage behaviour could explain why this species consumes prey soon after capture. In contrast, C. caroli constructs a permanent web and stores captured prey on a stabilimentum that may explain the very low incidence of immediate consumption of prey observed in this species.     

Some aspects of vulnerability to cyclopoid predation of zooplankton prey individuals

The predation cycle (encounter, attack, capture and ingestion or survival) by adult female Acanthocyclops robustus was observed for four crustacean prey types. The chief defense of A. robustus nauplii was escape response ability, reducing the probability of capture after attack, and, most likely, attack after encounter. The most important feature reducing the vulnerability of Ceriodaphnia and Daphnia species was large body size, decreasing the probability of capture after attack. Escape response ability and carapace strength/integrity further reduced vulnerability. Carapace strength/integrity was an effective defense for Bosmina longirostris, reducing the probability of ingestion after capture.The predation cycle by juvenile A. robustus was examined for three prey types. All three prey types seemed to be readily attacked. Due to their possession of loricae, Keratella cochlearis and Pompholyx sulcata were seldom eaten, while the illoricate Synchaeta kitina was highly vulnerable.Egg vulnerability after attack by the adult female predator was analysed. The eggs of Brachionus calyciflorus, Pompholyx sulcata and Filinia longiseta were rarely eaten, although the adults of the latter were usually ingested (thus causing the eggs to float free). Out of three attacks recorded on Keratella Quadrata, the eggs were eaten (or destroyed) twice.Handling times by the adult female predator were measured for a number of prey types. The shortest mean handling time was for Synchaeta kitina (less than one second), while the longest was on Ceriodaphnia species (716 seconds). Results were quite variable. Handling time was significantly positively related to prey body volume, while exoskeletal strength/integrity also increased this time. No effect of temperature on handling time was found for Synchaeta pectinata or Polyarthra major between 15 and 26.5 °C.     

Evolutionary trends in the androecium of theOrchidaceae

The evolution of the androecium in theOrchidaceae shows three major trends. There is a progressive trend in the degree of fusion of the filament(s) and staminode(s) to the gynoecium. Secondly, there is a reduction in the number of fertile anthers. Finally, there is a progressive change in the position of the base of the anther relative to the apex of the stigma; in the more primitive orchids the apex of the stigma is always higher than the base of the anther (this position is reversed in the higher orchids). All three trends reflect variation in the evolution of pollen dispersal and pollen reception mechanisms in theOrchidaceae. Trends in the evolution of the orchid anther(s) tend to parallel trends in the evolution of their pollinaria.     

Novel cost of a sexually selected trait in the rubyspot damselfly Hetaerina americana: conspicuousness to prey

Conspicuousness to predators frequently has been invoked asa cost of sexually selected traits, but conspicuousness to preyhas not We tested for the latter using rubyspot damselflies(Hetaerina americana) as the predator. Previous work on thisspecies showed that the red spots on male wings are intrasexuallyselected and reduce survival. Since female wings lack red spots,we first compared male and female weight gain rates per unithunting time. Females gained weight significandy faster thanmales in both mg per hour and relative to body weight. We thencompared the weight gain rates of females painted with red wingspots to those of control females painted with clear ink ornot manipulated. Controls gained weight significandy fasterthan red-painted females. Behavioral observations revealed thatred females attempted to capture prey at normal rates and experiencednormal rates of agonistic interference from conspecifics ofboth sexes. Nevertheless, red females captured fewer prey perminute and per capture attempt than did sham-manipulated andunmanipulated controls. We infer that the red spots reducedfemale weight gain rates by increasing their visibility to prey.Close similarity between male and red female weight gain ratesrelative to unmanipulated females suggests that red spots mayalso be a hunting handicap for males. [Behav Ecol 7: 465–473(1996)]     

Coevolution between crossbills and black pine: the importance of competitors,forest area and resource stability

Studies of predator‐prey interactions have found that geographically structured coevolution has played an important role in the adaptive diversification of crossbills (Loxia spp.). We extend those studies by considering common crossbills (L. curvirostra) in the Mediterranean where they rely on seeds in the cones of black pine (Pinus nigra). On the continent, where tree squirrels (Sciurus vulgaris) are present, enhanced defenses against crossbills were most evident in larger areas of pine forest. On islands in the absence of tree squirrels, crossbills and black pine have coevolved in a predator‐prey arms race on Cyprus but not Corsica. In contrast to other conifers that island endemic crossbills rely upon, black pine does not hold seeds in its cones year round. Consequently, key to the strong crossbill–pine interaction on Cyprus is likely the presence of an alternative conifer that provides seeds during early summer when black pine seeds are scarce.     

Appearances can be deceptive: different diversification patterns within a group of Mediterranean earthworms (Oligochaeta, Hormogastridae)

Many recent studies on invertebrates have shown how morphology not always captures the true diversity of taxa, with cryptic speciation often being discussed in this context. Here, we show how diversification patterns can be very different in two clades of closely related earthworms in the genus Hormogaster stressing the risk of using nonspecific substitution rate values across taxa. On the one hand, the Hormogaster elisae species complex, endemic to the central Iberian Peninsula, shows morphological stasis. On the other hand, a clade of Hormogaster from the NE Iberian Peninsula shows an enormous morphological variability, with 15 described morphospecies. The H. elisae complex, however, evolves faster genetically, and this could be explained by the harsher environmental conditions to which it is confined—as detected in this study, that is, sandier and slightly poorer soils with lower pH values than those of the other species in the family. These extreme conditions could be at the same time limiting morphological evolution and thus be responsible for the observed morphological stasis in this clade. Contrarily, Hormogaster species from the NE Iberian Peninsula, although still inhabiting harsher milieu than other earthworm groups, have had the opportunity to evolve into a greater morphological disparity. An attempt to delimit species within this group following the recently proposed general mixed Yule‐coalescent method showed a higher number of entities than expected under the morphospecies concept, most probably due to the low vagility of these animals, which considerably limits gene flow between distant conspecific populations, but also because of the decoupling between morphological and genetic evolution in the H. elisae complex.