Temperature affects male and female potential reproductive rates differently in the sex-role reversed pipefish, Syngnathus typhle

The differences in potential reproductive rate between the sexescan be used to predict the operational sex ratio and the patternsand intensity of mating competition and hence sexual selectionin a population. This article describes how one environmentalcomponent, temperature, affects potential reproductive ratesof the two sexes in the paternally brooding, sex-role reversedpipefish (Syngnathus typhle). Males brooded embryos much longer(on average 58 days) in cold water (about 10°C) than inwarmer water (35 days at about 15°C). As a consequence,the potential reproductive rate (number of eggs brooded perday) of males was significantly higher in warm water. In females,however, potential reproductive rate, i.e., number of eggs producedper day given an unlimited access to mates, was not significantlydifferent between temperatures. In both sexes, potential reproductiverate was positively related to body size. At both temperatures,females had the potential to reproduce faster than males. Asa result, the operational sex ratio will become female biasedand sex-roles reversed, as is the case in this species. Sincetemperature differently influenced the potential reproductiverates of males and females, with the sexual difference largerat lower temperatures, more intense female-female competitionis predicted at low temperatures.     

Vertical bars on male Xiphophorus multilineatus: a signal that deters rival males and attracts females

We examined the function of the vertical bar pattern on maleswordtails (Xiphophorus multilinneatus) as a signal in bothmale-male competition and female choice. This pattern had previouslybeen described as an aggressive signal because males intensifiedthe bars during male-male encounters in the laboratory. Ourfield observations supported this observation and also showedthat bars intensified when males courted females. The intensityof bars was correlated with access to females in the field.Within the size range of males that have bars, however, neitherbar number nor male size appeared to influence access to females.We used freeze-branding to remove the bars from males in thelaboratory so that we could control for characters correlatedwith bar intensity, and tested males and females separatelyso that we could separate the influence of these two componentsof sexual selection. We compared the responses of males andfemales to males that had their bars removed and control malesfreeze-branded between the bars. Test males responded more aggressivelyto males without bars as compared to control males. In addition,females showed a preference for control males over males thathad their bars removed. These results suggest that the barsmay function as a signal that deters rival males and attractsfemales.     

Relationships between food resources, foraging patterns, and reproductive success in the water pipit, Anthus sp. spinoletta

A basic but rarely tested assumption in optimal foraging theoryis that positive relationships exist between the foraging patternof an animal, its short-term benefits in feeding, and its long-termfitness. We present evidence for these relationships for a centralplace foraging situation. We studied the foraging behavior ofadult water pipits (Anthus sp. spinoletta) feeding nestlingsin an Alpine habitat near Davos, Switzerland, with the followingresults: (1) searching effort decreases with increasing distancefrom the nest, (2) the amount of prey and the proportion oflarge items brought to the nest increases with increasing foragingdistance, (3) water pipits do not forage according to habitatavailability, but prefer vegetation types with the highest fooddensity (mainly grass and herbs) and avoid those with the lowest,and (4) this selectivity is only expressed when the birds foragemore than 50 m from the nest, i.e., usually outside the territory.Among the several potential interpretations of these results,the most parsimonious is that foraging decisions are based onprofitability, i.e., on the net energy gain per time unit. Additionally,we found that food conditions translate into fitness: the numberof fledglings per nest is related positively to the averageprey biomass at the foraging place and negatively to the averagedistance between the foraging place and the nest. Maximum economicdistances, which were predicted from this food-fitness relationship,agreed well with the actual foraging distances observed. Thissuggests a dose connection between foraging decisions and fitness.In addition to the theoretical issues, some conservation issuesare also briefly discussed.     

Suppressed breeding in the field vole (Microtus agrestis): an adaptation to cyclically fluctuating predation risk

The densities of microtine rodents and their main predators,small mustelids, fluctuate synchronously in 3–5-year cyclesin central and northern Fennoscandia. Predation by small mustelidshas been suggested as one of the driving forces in microtinecyclicity, causing deep synchronous declines of several volespecies. We studied experimentally the effects of small mustelidson mating behavior, foraging, and breeding in nonwintered fieldvoles (Microtus agrestis) originating from a cyclic population.By using mustelid odors, we simulated a crash phase environmentwith high predation risk for breeding pairs of voles. In ourexperiments, 87% of the female field voles suppressed breedingwhen exposed to mustelid odors. Both female and male behaviorchanged, and no mating behaviors were observed under the simulatedpredation risk. Weights of both sexes decreased when exposedto mustelid odor, probably due to decreased foraging; weightsof the control females increased due to pregnancy; and no weightchanges occurred in control males. Decreased breeding and foragingpossibilities under high predation pressure may form the basisfor the ultimate explanation for breeding suppression. Thereare at least two different mechanisms for breeding suppression:either mating does not take place or malnutrition in femalesdoes not' allow breeding to occur. Delayed breeding under highrisk of predation, for whatever reason, could increase the probabilityof individuals, especially that of the females, to survive overthe crash to the next, safer breeding season when their youngwould have better possibilities to survive.     

Dominance, competition, and energetic reserves in the European starling, Sturnus vulgaris

We investigated the relationships between social dominance,competition for food, and strategies of body mass and fat regulationin the European starling (Sturnus vulgaris). In birds housedin groups of three, subdominant birds stored more fat than dominants.A removal experiment established a causal link between socialdominance and fat reserves; in groups that had the dominantindividual removed, the remaining birds reduced body mass andfat, relative to control groups that had the subordinate removed.In a second experiment, we investigated the influences of degreeof competition for food and dominance on body mass and fat reserves.Birds under high competition increased fat reserves and tendedto have higher body mass than birds under low competition. Theincrease in fat reserves was higher in the subdominants thanin the dominants. These results are consistent with hypothesesconcerning dominance-dependent access to food; subdominant birds,or birds under increased competition, may store more fat asan insurance against periods when food cannot be obtained. However,relations between dominance, body mass, and fat reserves mayalso arise through other proximate factors relating to dominance-dependentcosts and benefits of fat storage, such as predation risk andenergetic expenditure.     

Energetic constraints and foraging efficiency

Previous research considers foraging options that differ interms of their gross rate of gain b and rate of energy expenditurec. This research argues that maximizing efficiency b/c willmaximize net energetic gain when there is an upper limit onthe amount of energy that can be assimilated. This analysisdoes not include the expenditure during the time for which theanimal is unable to forage because of this constraint. Whenthis expenditure is included, maximizing efficiency is no longeroptimal. Instead the best feeding option is the one with thehighest value of b/(c – c₁), where c, is the metabolicrate when the animal is not foraging.     

Parental effort of kestrels (Falco tinnunculus) in nest defense: effects of laying time, brood size, and varying survival prospects of offspring

We studied the nest defense behavior of Eurasian kestrels (Falcotinnunculus) towards a stuffed pine marten (Martes martes) througha 3-year vole cycle (1990–92) in western Finland. Survivalprobability of offspring decreases with a later start of breeding,and, therefore, early breeders should protect their offspringmore than late ones. We found this true for males during theincubation period, but not for females. In addition, we expectedthe nest defense intensity to increase with offspring number.During the incubation period, this was true for females, butnot for males. During the nestling phase, parents did not adjusttheir defense effort to natural or manipulated (by one to twoyoung) brood size. Survival prospects of kestrel offspring werehighest in the increasing vole year 1991 and lowest in the decreasingvole year 1992, and, therefore, we expected the defense activityof kestrels to follow the same trend. However, the oppositeresult appeared true for females with a similar tendency formales. Most hypotheses predicting avian nest defense behaviorwere not supported by our data. Temporally heterogeneous environmentand low degree of nest-site tenacity of migratory kestrels maymake them unfamiliar with environmental variation and survivalprospects of their offspring. Therefore, fitness benefits ofparental care are not predictable, and kestrels may thus adjusttheir parental effort to their own future reproductive potential(i.e., number of future breeding attempts), rather than to somecurrent investment indicator, like offspring age and number.     

Adenylyl cyclase and G-proteins in Phytomonas

Phytomonas sp. membranes have an adenylyl cyclase activity which is greater in the presence of Mn2+ than with Mg2+. The Mg2+ and Mn2+ activity ratio varies from one membrane preparation to another, suggesting that the adenylyl cyclase has a variable activation state. A[35S]GTP-gamma-S-binding activity with a Kd of 171 nM was detected in Phytomonas membranes. Incubation of these membranes with activated cholera or pertussis toxin and [adenylate 23P]NAD+ led to incorporation of radioactivity into bands of about 40-44 kDa. Crude membranes were electrophoresed on SDS-polyacrylamide gels and analyzed, by Western blotting, with the 9188 anti-alpha[s] antibody and the AS/7 antibody (anti-alpha[i], anti-alpha[i1], and anti-alpha[i2]. These procedures resulted in the identification of polypeptides of approximately 40-44 kDa. Phytomonas adenylyl cyclase could be activated by treatment of membrane preparations with cholera toxin, in the presence of NAD+, while similar treatment with pertussis toxin did not affect this enzyme activity. These studies indicate that in Phytomonas, adenylyl cyclase activity is coupled to an unknown receptor entity through G alpha[s] proteins.     

Thidiazuron-induced adventitious shoot regeneration of sweetpotato (Ipomoea batatas)

Adventitious shoots of sweetpotato (Ipomoea batatas L. Lam.) were produced in vitro using a two-stage culture method. Petiole explants were incubated on Murashige and Skoog (MS) medium supplemented with 2,4-dichlorophenoxy acetic acid (0.2 mg·liter^−1) for 3 d, and transferred to MS medium with thidiazuron (0 to 0.4 mg·liter^−1). Shoot regeneration was observed in most explants (78.2%) of genotype PI 318846-3 within 28 days when cultured on thidiazuron at 0.2 mg·liter^−1. Histological studies of cultured petiole explants showed meristematic activity within cells of vascular bundles and throughout the ground tissue. Explants isolated from apical leaves exhibited higher shoot regeneration frequency than those isolated from the basal portion of the shoot. Leaf lamina explants exhibited lower frequency of regeneration than petiole explants. In contrast to thidiazuron, the use of zeatin riboside, and kinetin resulted in a lower frequency of shoot regeneration although more sweetpotato genotypes could be regenerated using either of these two cytokinins. The sweetpotato plants regenerated using thidiazuron grew vigorously and rooted easily when transferred to the greenhouse.