Facultative placentotrophy: half-way house or strategic solution?

While yolk is generally the primary source of embryo nutrients in squamates, numerous species supplement this with facultative placentotrophy. We argue that facultative placentotrophy should have selective importance relevant to offspring fitness. In the skink Niveoscincus metallicus, the size of ovulated eggs is unrelated to maternal size but large females produce offspring that are larger than is necessary for survival, providing evidence for facultative placentotrophy. We discuss the circumstances in which facultative placentotrophy might be used to supplement the nutritional support provided by yolk and obligate placentotrophy in this species, and present summary data from experiments designed to investigate these circumstances. Clutch reduction by oviduct removal had no effect on neonate mass or snout-vent length, indicating that the number of embryos does not influence allocation of maternal resources once gestation has commenced. Manipulation of maternal basking opportunity in combination with food intake during pregnancy suggested that an important role of facultative placentotrophy is the optimization of embryonic fat reserves. This hypothesis was supported by the observation that larger neonates have larger abdominal fat bodies. These reserves presumably facilitate survival in the relatively short pre-hibernatory period available to newborn animals. Our data indicate that they also play a vital role in maintaining pre-natal condition if birth is delayed by adverse weather, a common circumstance in this species. In such circumstances the yolk has been used up and the placental membranes have degenerated. Experimental induction of premature ovulation of eggs with reduced yolk, achieved by injecting females with FSH, was followed by fertilization using stored sperm. Gestation length was greatly reduced and the resulting neonates were all < or =75% normal birth mass, with two of the six births being stillborn. Thus facultative placentotrophy does not appear to be a means of compensating for a poor yolk supply. We suggest that facultative placentotrophy in N. metallicus is not a transitional stage en route to greater reliance on obligate placentotrophy, but a uniquely squamate adaptation that provides flexibility in embryonic nutrition, and optimizes offspring fitness in an unpredictable temperate climate.     

The use of internal nitrogen stores in the rhizomatous grass Calamagrostis epigejos during regrowth after defoliation

BACKGROUND AND AIMS: The regrowth dynamics after defoliation of the invasive grass Calamagrostis epigejos were studied. As nitrogen (N) reserves have been shown to play an important role during plant regrowth, the identity, location and relative importance for regrowth of N stores were determined in this rhizomatous grass. METHODS: Plant growth, nitrate uptake and root respiration were followed during recovery from defoliation. Water soluble carbohydrates, nitrate, free amino acids and soluble proteins were analysed in the remaining organs. KEY RESULTS: Nitrate uptake and root respiration were severely reduced during the first days of regrowth. Roots were the main net source of mobilized N. The quantitatively dominant N storage compounds were free amino acids. Free amino acids and soluble proteins in the roots decreased by 55 and 50%, respectively, and a substantial (approximately 38%) decrease in stubble protein was also observed. Although the relative abundance of several soluble proteins in roots decreased during the initial recovery from defoliation, no evidence was found for vegetative storage protein (VSP). Furthermore, rhizomes did not act as a N storage compartment. CONCLUSIONS: Production of new leaf area was entirely reliant, during the first week after defoliation, on N stores present in the plant. Mobilized N originated mainly from free amino acids and soluble proteins located in roots, and less so from proteins in stubble. Presence of VSP in the roots was not confirmed. The data suggest that rhizomes played an important role in N transport but not in N storage.     

Competing dwarf males: sexual selection in an orb-weaving spider

Hypotheses for the adaptive significance of extreme female-biased sexual size dimorphism (SSD) generally assume that in dimorphic species males rarely interfere with each other. Here we provide the first multivariate examination of sexual selection because of male-male competition over access to females in a species with 'dwarf' males, the orb-weaving spider Argiope aurantia. Male A. aurantia typically try to mate opportunistically during the female's final moult when she is defenceless. We show that, contrary to previous hypotheses, the local operational sex ratio (males per female on the web) is male-biased most of the season. Both interference and scramble competition occur during opportunistic mating, the former leading to significant selection for large male body size. Male condition and leg length had no effect on mating success independent of size. We discuss these findings in the context of the evolution of extreme female-biased SSD in this clade.     

MEK inhibitors block AICAR-induced maturation in mouse oocytes by a MAPK-independent mechanism

The present study was carried out to assess the possible role of mitogen-activated protein kinase (MAPK) in the meiosis-inducing action of the AMP-activated protein kinase (AMPK) activator, 5-aminoimidazole-4-carboxamide 1-beta-ribofuranoside (AICAR). Cumulus cell-enclosed oocytes (CEO) or denuded oocytes (DO) from immature, eCG-primed mice were cultured 4 hr in Eagle's minimum essential medium containing dbcAMP plus increasing concentrations of AICAR or okadaic acid (OA). OA is a phosphatase inhibitor known to stimulate both meiotic maturation and MAPK activation and served as a positive control. Both OA and AICAR were potent inducers of meiotic resumption in mouse oocytes and brought about the phosphorylation (and thus, activation) of MAPK, but by different kinetics: MAPK phosphorylation preceded GVB in OA-treated oocytes, while that resulting from AICAR treatment appeared only after GVB. The MEK inhibitors, PD98059 and U0126, blocked the meiotic resumption induced by AICAR but not that induced by OA. Although the MEK inhibitors suppressed MAPK phosphorylation in both OA- and AICAR-treated oocytes, meiotic resumption was not causally linked to MAPK phosphorylation in either group. Furthermore, AICAR-induced meiotic resumption in Mos-null oocytes (which are unable to stimulate MAPK) was also abrogated by PD98059 treatment. A non-specific effect of the MEK inhibitors on AICAR accessibility to the oocyte was discounted by showing that they failed to suppress either nucleoside uptake or AICAR-stimulated phosphorylation of acetyl CoA carboxylase (ACC), a substrate of AMPK. The suppression of AICAR-induced maturation by MEK inhibitors must, therefore, be occurring by actions unrelated to MEK stimulation of MAPK; consequently, it would be prudent to consider this possible non-specific action of the inhibitors when they are used to block MAPK activation in mouse oocytes.     

Winter survival of age-0 smallmouth bass, <Emphasis Type="Italic">Micropterus dolomieu</Emphasis>, in north eastern lakes

We examined the winter survival of age-0 smallmouth bass,Micropterus dolomieu, in lakes at their northern limit of distribution in New Brunswick, Canada. Pre- and post-winter collections over a 3 year period suggested the smallest individuals, <50 mm total length, died during winter under ice. Experiments with wild, age-0 smallmouth bass held in lakes demonstrated a size-dependent survival where smaller individuals had greater survival with an increasing temperature of exposure, but the largest individuals had reduced survival at warmer temperatures. Survivors lost 22–54% of pre-winter energy reserves measured as ash-free dry weight, which was similar to wild individuals captured in spring. Body size at the onset of winter affects survival, but it also appears that temperature interacting with a suite of environmental and biological factors affect changes in energy use and therefore survival of age-0 smallmouth bass under ice in winter.     

The importance of nitrogen and carbohydrate storage for plant growth of the alpine herb Veratrum album

We examined whether nitrogen (N) and carbohydrates reserves allow Veratrum album, an alpine forb, to start spring growth earlier than the neighbouring vegetation and to survive unpredictable disturbances resulting in loss of above-ground biomass. * Seasonal dynamics of plant reserves, soil N availability and vegetation growth were monitored. Veratrum album shoots were experimentally removed when carbohydrate reserves were at a seasonal minimum and the subsequent changes in biomass and reserves were compared with those in control plants. Reserves did not give V. album a competitive advantage in spring; however, they did function as a buffer against the impact of calamities. Shoot removal resulted in significantly lower root dry weight, higher N concentration in rhizome and roots and lower starch concentrations in rhizome and roots but no plant mortality was observed. Veratrum album used stored N reserves to supplement N uptake and establish high leaf N concentrations, which facilitated a rapid refilling of depleted carbohydrate reserves. The primary function of N reserves appears to be to allow V. album to complete the growing cycle in as short a period as possible, thus minimizing exposure to above-ground risks.     

The importance of urban reserves for conserving beetle communities: a case study from New Zealand

Urban reserves provide a major opportunity for conservation of indigenous biodiversity in the heavily urbanised landscape of Waitakere City (Auckland), New Zealand. However, there is little documented information on what indigenous fauna survives in these reserves. Beetle (Coleoptera) communities associated with two small, isolated urban reserves and two sites in a larger forest area within the Waitakere Ranges were sampled using pitfall traps and analysed. A total of 887 beetles, from 23 families and 89 recognisable taxonomic units were caught. The urban reserves had a marked reduction in species richness and abundance of beetles compared with the sites within the larger forest areas. Various environmental factors influencing the distribution of beetles across the sites were investigated. The most important factors were size of fragment, local forest cover and soil moisture. Common species (>5 specimens in the total dataset) found in the Waitakere Ranges and small urban reserves, were either endemic or indigenous to New Zealand. Therefore, even though these reserves may be isolated from a larger, more continuous forest tract, they have considerable potential as reservoirs of beetle diversity in highly modified landscapes and the contribution of urban reserves to the local sustainability of beetle assemblages emphasises the importance of maintaining green areas in and around cities.     

From anther and pollen ripening to pollen presentation

The events and processes occurring between pollen maturation, opening of the anther and presentation of pollen to dispersing agents are described. In the final phases of pollen development, starch is always stored; this occurs before the anther opens. Depending on the species, this starch may be totally or partially transformed into: (a) other types of polysaccharides (fructans and rarely callose); (b) disaccharides (sucrose); (c) monosaccharides (glucose and fructose, all situated in the cytoplasm. While awaiting dispersing agents and during dispersal, polysaccharides, especially fructans, and sucrose may be interconverted to control osmotic pressure and prevent loss and uptake of water. Opening of the anther is preceded by disappearance of the locular fluid and in many cases by partial dehydration of the pollen. Pollen generally has a water content between 5 and 50%. Pollen with a high water content may or may not be able to control water retention during pollen exposure and dispersal. Pollen may be dispersed in monads or grouped in pollen dispersing units by the following mechanisms: (i). tangling of filamentous pollen; (ii). adhesion by viscous substances (pollenkitt, tryphine, elastoviscin) derived from the tapetum; (iii). common walls. When the anther opens, the pollen may be dispersed immediately, remain until dispersed (primary presentation), or be presented to pollinators in another part of the flower (secondary presentation).     

On the fraction of habitat allocated to marine reserves

The case for marine reserves is strengthening, and both deterministic and stochastic calculations show that fisheries management using reserves may achieve harvests comparable with management without reserves. Thus, depending upon the metric used, reserves need not disadvantage harvest. Reserves provide a buffer that increases the chances of sustainability of the stock, and thus the fishery. In this paper, I develop methods (deterministic and stochastic) that allow one to determine how much habitat needs to be set aside as reserve, once societal decisions concerning the goals of reserves are made. The answer to the question: "how much habitat needs to be allocated to reserves" is not a simple single number. Rather, it is a procedure that can be employed once biological, operational and social information are provided. The methods also apply to reserves used to aid stock recovery.     

Physiology and development of the M and S molecular forms of Anopheles gambiae in Burkina Faso (West Africa)

In West Africa, M and S molecular forms of Anopheles gambiae sensu stricto (Diptera: Culicidae) Giles, frequently occur together, although with different population bionomics. The S form typically breeds in rain‐dependant water collections and is present during the rainy season only whereas the M form can thrive all year long in areas with permanent breeding opportunities. In the present study, we explored physiological and developmental trade‐offs at play in laboratory colonies and field populations of the M and S forms that originated from an area of sympatry in Burkina Faso, where M and S larvae exhibit such habitat segregation. In the laboratory, larvae of the M form developed slower than the S form (mean values 9.51 and 8.85 days, respectively, Wilcoxon's test, P < 0.001). Although wing length and dry weight at emergence showed large variations, M females were on average 8% heavier than S females of similar wing length. Higher nutritional reserves (proteins and lipids) in teneral adults explained part of this weight difference, reflecting a better ability of the M form to garner resources at the larval stage. Furthermore, a higher rate of ovarian maturation was observed in the M form after a single bloodmeal. The relevance of these findings for parasite transmission is discussed.