Sperm size and number variation in the red flour beetle

Disruptive selection between large, nutritive gametes and numerous, competing gametes may have driven the evolution and maintenance of anisogamy. Sperm competition can explain why there are so many tiny sperm because numerical competition between rival gametes drives males to maximize sperm number and this may be achieved by minimizing sperm size. Since males operate within a finite reproductive budget and ejaculate production is limited, we might predict that, when variation in sperm size exists, males must trade increases in sperm size against a decrease in sperm number. We use Tribolium castaneum as our model to investigate the existence of a sperm size-number trade-off. We sampled 14 different populations that have been isolated for different periods (up to 39 years) and find across this sample of 70 males that there is significant variation in both sperm length and ejaculate sperm number between males. Despite this significant variance, we find no evidence for any relationship between sperm size and number across males. There is some evidence for a trade-off when we analyse across 14 population means, but this relationship is not robust and disappears when a single outlier is omitted. We conclude that sperm size and ejaculate sperm number vary independently, but that differential allocation to gonadal tissue and/or ejaculation frequency would permit this independent variation.     

The Effects of Winter Burning and Grazing on Resources and Survival of Texas Horned Lizards in a Thornscrub Ecosystem

ABSTRACT The ecological effects of land-use practices on reptiles, especially endangered or threatened species, are of conservation and scientific interest. We describe the effects of rotational livestock grazing and prescribed winter burning on resources and survival of the Texas horned lizard (Phrynosoma cornutum) during the summers of 1998 to 2001 in southern Texas, USA. We evaluated survival rates of Texas horned lizards (n = 111) on 6 study sites encompassing 5 different burning and grazing treatments. We also measured indices of cover (i.e., vegetation) and food abundance (i.e., harvester ants [Pogonomyrmex rugosus]). We telemetered and relocated adult lizards daily. We divided the study into 2 seasons, spring (15 Apr–30 Jun) and summer (1 Jul–15 Aug), corresponding to the relative activity of horned lizards. Winter burning provided an increase in food resources and led to increased survival of Texas horned lizards in the second growing season after fire, but grazing-induced changes in vegetation cover reduced survival, likely by increasing lizard vulnerability. Fire and grazing reduced litter and increased bare ground and forb cover but did not affect woody vegetation. Ant activity was greater in burned sites and varied with grazing level, season, and year. Summer survival functions of horned lizards varied by burning treatment, with higher survival observed on burned sites in the second year after burning. Survival rates were ordered from highest in ungrazed sites to lowest in heavily grazed sites. We recognize the limitations of our work resulting from a lack of spatial replication of treatments. However, our mensurative study provides fertile ground for future hypothesis testing regarding the effects of land management on shrubland and grassland reptiles. We propose that future studies focus on the population consequences of variation in burn frequency, burn timing, and grazing intensity.     

Influence of Roads,Rivers, and Mountains on Natal Dispersal of White-Tailed Deer

Abstract: Natural and anthropogenic landscape features, such as rivers, mountain ranges, and roads can alter animal dispersal paths and movement patterns. Consequently landscape, through its effects on dispersal, may influence many ecological processes, including disease transmission, invasion dynamics, and gene flow. To investigate influences of landscape features on dispersal patterns of a large mammal, we captured and radiomarked 363 juvenile male white-tailed deer (Odocoileus virginianus), including 212 confirmed dispersers, in 2 topographically dissimilar study areas in Pennsylvania, USA. Dispersal azimuths were uniformly distributed in the western study area (WSA), where there was irregular, hilly topography. Mean dispersal azimuths paralleled ridge direction in the eastern study area, where long parallel ridges were aligned northeast-southwest. Major roads in both areas and a large river in the WSA were semipermeable barriers to dispersal of juvenile males; dispersal paths were less likely to intersect these linear features. Dispersal movements were direct and brief, typically lasting <12 hours. For all dispersers, we found no evidence for preference or avoidance of establishing adult, postdispersal ranges in proximity to roads; however, deer that encountered roads near the terminus of their dispersal path were more likely to stop on the near side. Further, for deer that established postdispersal home ranges near major roads, these features influenced range placement such that locations were typically clustered on one side of the road. The influence of roads, rivers, and mountains on dispersal paths and postdispersal locations of white-tailed deer suggest that landscape-specific features should be considered in conservation and management of this and possibly other species of large mammals.     

Larval experience induces adult aversion to rearing host plants: a novel behaviour contrary to Hopkins' host selection principle

1. Hopkins' host selection principle (HSP) states that insects should prefer foliage from their rearing host plant over that of an alternative host. 2. The current study tested whether eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), that were laid and developed on, respectively, resistant and susceptible white spruce Picea glauca (Moench) Voss, showed differences in their feeding and oviposition preferences for these two hosts. 3. The data revealed that previous experience of spruce budworm on a host tree type does not influence the host acceptance and feeding behaviour of later larval stages. However, adult budworm reared on resistant white spruce needles preferentially selected susceptible white spruce needles as the host for their progeny, whereas those reared on susceptible needles showed no preference. 4. To the authors' knowledge, this is the first report of an insect showing an oviposition preference for the non‐rearing host plant. This would tend to increase mixing between insects from susceptible and resistant trees. The present results thus argue against Hopkins' HSP and suggest that learned aversion to resistant foliage experienced by larvae is carried into the adult stage.     

Strong population structure characterizes weediness gene evolution in the invasive grass species Brachypodium distachyon

Mediterranean annual grasses have invaded California and have replaced vast areas of native grassland. One of these invasive grasses is Brachypodium distachyon , a new model species for the grasses with extensive genomic resources and a nearly completed genome sequence. This study shows that the level of genetic variation in invaded California grasslands is lower compared to the native range in Eurasia. The invaded regions are characterized by highly differentiated populations of B. distachyon isolated by distance, most likely as a result of founder effects and a dearth of outcrossing events. EXP6 and EXP10 encoding α-expansins responsible for rapid growth, and AGL11 and AGL13 encoding proteins involved in vegetative phase regulation, appear to be under purifying selection with no evidence for local adaptation. Our data show that B. distachyon has diverged only recently from related Brachypodium species and that tetraploidization might have been as recent as a few thousand years ago. Observed low genetic variation in EXP10 and AGL13 appears to have been present in Eurasia before tetraploidization, potentially as a result of strong selective pressures on advantageous mutations, which are most likely responsible for its fast growth and rapid completion of its life cycle.     

SIMPLIFIED CAPACITANCE MONITORING FOR THE DETERMINATION OF CAMPYLOBACTER SPP. GROWTH RATES

Capacitance monitoring is commonly used as an efficient means to generate growth curves of bacterial pathogens. However, the use of capacitance monitoring with Campylobacter spp. was previously determined to be difficult due to the complexity of the required media. We investigated capacitance monitoring using a simplified medium for the efficient and reproducible construction of growth curves for Campylobacter spp . It was determined that Campylobacter spp. should initially be propagated on Mueller Hinton plates in a microaerobic atmosphere (5% O₂, 10% CO₂, 85% N₂) at 37C for 24 h, followed by transfer to Mueller Hinton biphasic cultures for 6 h at 37C in a microaerobic atmosphere. Serial dilutions of the Campylobacter spp. cultures should be used for inoculation of Bactometer wells that contain 1 mL Mueller Hinton broth supplemented with 0.1 M sodium pyruvate for the completion of Campylobacter spp. growth curves with the Bactometer.

PRACTICAL APPLICATIONS

Growth rates can vary greatly among Campylobacter isolates; therefore, the rapid and reproducible methods described will prove useful in studies where the generation of growth curves is critical for subsequent experimental analyses.     

Colleterial glands of Sesamia nonagrioides as a source of the host-recognition kairomone for the egg parasitoid Telenomus busseolae

Abstract.  The maize stemborer Sesamia nonagrioides glues its egg masses under the leaf sheaths or ear bracts using colleterial gland secretion. In spite of such concealed oviposition sites, these eggs are parasitized by Telenomus busseolae. The colleterial glands of S. nonagrioides are investigated as a possible source of the host-recognition kairomone for T. busseolae . This secretion, applied on glass beads, elicits intense antennal drumming and oviposition probing behaviour in the parasitoid. Through an histochemical study, neutral and acid glycoconjugates are identified as components of the secretion. Finally, using ultrastructural techniques, the colleterial glands are described and classified as comprising class 3 secretory cells.