Life history strategies in a fluctuating environment: establishment and reproductive success in the arctic fox

Natal dispersal, territoriality and reproductive success can have a major impact on the range, genetics and risk of extinction of a population. The proportions of animals that disperse have often been investigated, but not their fate. We have studied the lifetime reproductive success of arctic foxes that successfully emigrated, travelled and settled. Of these, some settled in the vicinity of their natal site as residents and some immigrated from other areas, i.e. short- and long-range dispersers respectively. We found no sex bias in migration patterns. In presaturation years, more immigrants than residents settled. Immigrant females had higher reproductive success than resident females. There was strong support for the ultimate hypothesis of Competition For Resources (CFR), but not for the hypotheses of Competition For Mates (CFM), Resident Fitness (RFH) and Inbreeding Avoidance (IA). Our data on arctic foxes could not be fully explained by any of four proximate hypotheses. We suggest that the reason is that dispersal and establishment should be considered as state dependent life history characteristics of individuals rather than population averages.     

Life history traits of adults and embryos of the Antarctic midge Belgica antarctica

Although larvae of the Antarctic midge, Belgica antarctica, live for more than 2 years, the adult and embryonic stages are brief and are less well known than the larvae. In this report, we provide additional details of these understudied life stages with laboratory observation on adult emergence, longevity, preoviposition period and embryonic development. Male adults emerged slightly earlier than females, and they also lived longer. More than a half (57 %) of the adults that emerged in the laboratory were males. Females produced only a single egg mass and died within a day after oviposition. Embryonic development required 16 days at 4 °C, and prior to hatching, the pharate larvae perform a distinct sequence of behaviors that include drinking and peristaltic movement. We also discuss points that need to be resolved for laboratory propagation of this species.     

Life tables and reproductive parameters of Lutzomyia spinicrassa (Diptera: Psychodidae) under laboratory conditions

Lutzomyia spinicrassa is a vector of Leishmania braziliensis in Colombia. This sand fly has a broad geographical distribution in Colombia and Venezuela and it is found mainly in coffee plantations. Baseline biological growth data of L. spinicrassa were obtained under experimental laboratory conditions. The development time from egg to adult ranged from 59 to 121 days, with 12.74 weeks in average. Based on cohorts of 100 females, horizontal life table was constructed. The following predictive parameters were obtained: net rate of reproduction (8.4 females per cohort female), generation time (12.74 weeks), intrinsic rate of population increase (0.17), and finite rate of population increment (1.18). The reproductive value for each class age of the cohort females was calculated. Vertical life tables were elaborated and mortality was described for the generation obtained of the field cohort. In addition, for two successive generations, additive variance and heritability for fecundity were estimated.     

Life cycle and reproductive parameters of Clerada apicicornis signoret (Hemiptera: Lygaeidae) under laboratory conditions

The life cycle of Clerada apicicornis was determined under laboratory conditions. Mean development times in days were: egg 27.2, nymph I 12.5, nymph II 12, nymph III 13.4, nymph IV 16.4, nymph V 26. The life expectancy of adults ranged from 117 to 317 days (mean 196 days). Based on a cohort of 29 females of C. apicicornis, a horizontal life table was constructed. The following predictive parameters were obtained: net rate of reproduction (Ro = 48.31), intrinsic rate of population increase (r(m) = 0.153), generation time (Tc = 28.20 weeks), and finite rate of population increment (lambda = 1.16). The reproductive value (Vx) for each age class of the cohort females was calculated. The following observed parameters were calculated after mortality in each stage: net rate of reproduction (R'o=13.4), intrinsic rate of population increase (r c' =0.09 ), and finite rate of population increment (lambda' =1.1). The generation time (Tc' =27.4) was estimated using the methods of Laughlin and Bengstron. A vertical life table was elaborated and mortality was described for one generation of the cohort.     

Life history of the sand fly vector Lutzomyia cruciata in laboratory conditions

Lutzomyia cruciata Coquillet (Diptera: Psychodidae: Phlebotominae) is a potential vector of Leishmania sp.; its geographical distribution in Mexico is widespread, but its life history is unknown. The present study gives relevant information on the life cycle, morphology, survival and reproduction of Lu. cruciata observed over successive generations under laboratory conditions. Seven successive generations were produced. A total of 975 adults were obtained in a sexual proportion of 1.1 : 1 (female : male). Each Lu. cruciata female produced 20.7 eggs and 1.9 adults, approximately, with a proportion of eggs per female of 2.7% (first generation) and 21.3% (second generation). The life cycle of Lu. cruciata, from egg to adult, occurred in 52.7 ± 0.52 days. The largest percentage of mortality occurred during the egg stage (48.5%) and the first larval instar (26.5%), whereas in the pupal stage mortality was the lowest (9.1%). Lutzomyia cruciata exhibits sexual dimorphism based on size, which is exhibited as of the second larval instar, males being smaller than females. The maximum survival of females and males was 10 and 15 days, respectively. An overview of the immature stages of the species made with an electronic scanning microscope is included. This paper contributes basic information on aspects of Lu. cruciata that were previously unknown related to its life history.     

Life history of Paracoccus marginatus (Hemiptera: Pseudococcidae) on four host plant species under laboratory conditions

Life history of the mealybug, Paracoccus marginatus Williams and Granara de Willink, on three ornamental plants [Hibiscus rosa-sinensis L., Acalypha wilkesiana (Muell.-Arg.), and Plumeria rubra L.] and one weed species (Parthenium hysterophorus L.) was studied under laboratory conditions. Mealybugs were able to develop, survive, and reproduce on all four hosts; however, there were differences in the life history parameters. Adult females that developed on acalypha and parthenium emerged approximately 1 d earlier than those that developed on hibiscus and plumeria. Adult males had a longer developmental time on plumeria than on the other hosts. Survival of first- and second-instar nymphs and cumulative adult survival were lowest on plumeria. Longevity was not affected by hosts for males and females and averaged 2.3 +/- 0.1 and 21.2 +/- 0.1 d, respectively. On plumeria, 58.9 +/- 1.7% of the adults were females, which was a higher female percentage than on the other hosts. No egg production occurred in virgin females. Prereproductive and reproductive periods of the females were not affected by hosts and averaged 6.3 +/- 0.1 and 11.2 +/- 0.1 d, respectively. Mean fecundity of 186.3 +/- 1.8 eggs on plumeria was lower than on the other three plant species. Life history parameters of P. marginatus on hibiscus, acalypha, plumeria, and parthenium show its ability to develop, survive, and reproduce on a wide variety of plant species.     

Reproductive and post‐reproductive life history of wild‐caught Drosophila melanogaster under laboratory conditions

The life history of the fruit fly (Drosophila melanogaster) is well understood, but fitness components are rarely measured by following single individuals over their lifetime, thereby limiting insights into lifetime reproductive success, reproductive senescence and post‐reproductive lifespan. Moreover, most studies have examined long‐established laboratory strains rather than freshly caught individuals and may thus be confounded by adaptation to laboratory culture, inbreeding or mutation accumulation. Here, we have followed the life histories of individual females from three recently caught, non‐laboratory‐adapted wild populations of D. melanogaster. Populations varied in a number of life‐history traits, including ovariole number, fecundity, hatchability and lifespan. To describe individual patterns of age‐specific fecundity, we developed a new model that allowed us to distinguish four phases during a female's life: a phase of reproductive maturation, followed by a period of linear and then exponential decline in fecundity and, finally, a post‐ovipository period. Individual females exhibited clear‐cut fecundity peaks, which contrasts with previous analyses, and post‐peak levels of fecundity declined independently of how long females lived. Notably, females had a pronounced post‐reproductive lifespan, which on average made up 40% of total lifespan. Post‐reproductive lifespan did not differ among populations and was not correlated with reproductive fitness components, supporting the hypothesis that this period is a highly variable, random ‘add‐on’ at the end of reproductive life rather than a correlate of selection on reproductive fitness. Most life‐history traits were positively correlated, a pattern that might be due to genotype by environment interactions when wild flies are brought into a novel laboratory environment but that is unlikely explained by inbreeding or positive mutational covariance caused by mutation accumulation.     

Reproductive traits of Monochamus galloprovincialis (Coleoptera: Cerambycidae) under laboratory conditions

The pine sawyer Monochamus galloprovincialis (Olivier) is the vector of the introduced pine wood nematode Bursaphelenchus xylophilus (Steiner & Bührer) Nickle in Portugal, and until recently was considered a secondary forest insect. Under laboratory conditions, a study of biological and reproductive traits of 37 insect pairs was conducted. The longevity of both sexes was similar, being 61.2+/-6.5 days for males and 64.0+/-6.3 days for females (mean+/-SE). Sixteen small-sized insects (22% of the population) died within 20 days and before starting to reproduce. The sexual maturation period (without egg laying) was 20.4+/-0.7 days (mean+/-SE), while the oviposition period lasted 54.0+/-4.2 days (mean+/-SE). The oviposition rate increased very quickly during the first weeks of life, peaking to almost two eggs per day during days 30-44, and gradually dropping in the following weeks. The females laid an average of 67.0+/-5.96 (mean+/-SE) eggs through their lives. The hatch rate was 92.6+/-1.0% (mean+/-SE). There were large individual variations in longevity and fecundity parameters, and principal component analysis based on 16 morphological and biological parameters separated the breeding insects into four distinct groups. Almost half of the reproducing beetles were large-sized insects, with high longevity and fecundity traits. Overall, the reproductive potential of the Portuguese population of M. galloprovincialis seems to be smaller than that described for other Monochamus vectors of the pine wood nematode both in North America and Japan.     

Life history traits variation in heterogeneous environment: The case of a freshwater snail resistance to pond drying

Ecologists and population geneticists have long suspected that the diversity of living organisms was connected to the structure of their environment. In heterogeneous environments, diversifying selection combined to restricted gene flow may indeed lead to locally adapted populations. The freshwater snail, Galba truncatula, is a good model to address this question because it is present in a heterogeneous environment composed of temporary and permanent waters. In order to test the selective importance of those environments, we proposed here to measure survival of lineages from both habitats during drought episodes. To this purpose, we experimentally submitted adults and juveniles individuals from both habitats to drought. We found a difference in desiccation resistance between temporary and permanents waters only for adults. Adults from temporary habitats were found more resistant to drought. This divergence in desiccation resistance seems to explain the unexpected life history traits differences between habitats observed.     

How are the life history strategies of Antarctic terrestrial invertebrates influenced by extreme environmental conditions?

1. 1. Features of life history strategies of Antarctic terrestrial invertebrates are reviewed and compared with the predictions of two widely-used general life history models.

2. 2. Many features observed are consistent with the predictions of “adversity-” or “stress-selected” life histories, although “ruderal” characteristics are also observed.

3. 3. Many features are plesiotypic for the taxonomic groups concerned, suggesting a lack of evolved adaptations within the Antarctic biota.

4. 4. A large degree of flexibility is found in the life histories; this flexibility itself may allow passage of environmentally-imposed selective filters limiting colonisation and development in isolated and extreme terrestrial habitats.

5. 5. In general, Antarctic terrestrial invertebrates may be regarded as pre-adapted for survival of the various stresses imposed by their extreme environment.

     

Growth and survival strategy of the Antarctic mite Alaskozetes antarcticus

Growth and mortality rates of three juvenile instars and adults of the oribatid mite Alaskozetes antarcticus were measured over a twelve month period using field enclosures m Its maritime Antarctic habitat A pattern was found of rapid growth during the short summer period (0 2-0 4 μg dry weight increment per day) followed by gradual weight loss overwinter Most individuals completed one instar per year, reaching a premoult resting phase by late summer, with the moult being delayed and relatively synchronised early the next summer A small proportion of proto- and deutonymphs completed two moults within one summer period After the final moult adults overwintered again before commencing oviposition, suggesting that the life cycle (egg-egg) will take at least five years Mortality was not biased towards any instar or time of year Highest individual growth rates were obtained at a constant temperature of 7°C in the laboratory However expenmentai increase of mean field temperature from 2 7 to 4 3°C by use of a plastic cloche led to decreased growth, although no change in moulting frequency or mortality rate Laboratory survival was greatest at 2°C and decreased with increasing temperature
Alaskozetes antarcticus may be descnbed as 'a' (adversity) selected, showing an exceptionally long life cycle of five to six years and extensive physiological investment in survival adaptations Moult synchronisation in early summer, involving entering winter in the inactive premoult phase, will increase overwinter survival by reducing the chance of inoculative freezing from gut contents, and may be advantageous in maximising the time available for feeding during the subsequent summer, or ensuring proximity of the sexes after the final moult     

Life history traits of Aedes caspius (Diptera: Culicidae): a laboratory study of larval stages

The larval survival and development times of Aedes caspius (Diptera: Culicidae) were examined in the laboratory. These life history traits were estimated using life tables constructed for two populations, one of which had been subjected to a long-term larvicide control program. Traits were evaluated for eight different population densities. The effects of population, larval stage and larval density were investigated using a general linear model. Density was positively correlated with larval survival but did not affect development time. The fourth instar and pupae had the lowest larval survival rates. First and fourth instar larvae had the longest development times. These traits were not significantly different between the two populations. The effect of larvicide control on these traits is discussed.     

Life history and the competitive environment: trajectories of growth,maturation, and reproductive output among chacma baboons

The social environment is a key feature influencing primate life histories. Chacma baboons (Papio hamadryas ursinus) are a female-bonded species with a strict linear dominance hierarchy. In this species, the allocation of energy to competing demands of growth and reproduction is hypothesized to vary as a function of competitive ability, which in turn increases with social rank. Since growth rate is a major component of life history models, measures of age-specific growth were used to analyze variation in life history traits across social ranks. Weights of 42 immature baboons were obtained without sedation or baiting from a troop of well-habituated chacma baboons in the Okavango Delta, Botswana. Using demographic and weight data from this wild population, five main findings emerged: 1) Weight for age and growth rate of infant and juvenile females are positively associated with maternal rank. 2) Male growth is not influenced by maternal rank. 3) Female growth shows smaller variation across feeding conditions than male growth. 4) Low-ranking adult females continue investment in offspring through prolonged lactation until they reach a weight comparable to that of high-ranking infants. 5) The benefit of rank to reproductive success shown in this study is 0.83 additional offspring. Reproductive span determined predominantly by age at maturation contributes 27-38% to the difference in expected number of offspring by rank, vs. 62-73% due to reproductive rate. These findings have major implications for understanding the role of social environment in phenotypic plasticity of life history traits, and in the evolution of primate life histories.     

Temperature preferences of the mite, Alaskozetes antarcticus, and the collembolan, Cryptopygus antarcticus from the maritime Antarctic

Abstract. The thermal preferences of Alaskozetes antarcticus (Acari, Cryptostigmata) and Cryptopygus antarcticus (Collembola, Isotomidae) were investigated over 6 h within a temperature gradient (?3 to +13 °C), under 100% relative humidity (RH) conditions. After 10 days of acclimation at ?2 or +11 °C, individual supercooling points (SCP) and thermopreferences were assessed, and compared with animals maintained for 10 days under fluctuating field conditions (?6 to +7 °C). Acclimation at ?2 °C lowered the mean SCP of both A. antarcticus (?24.2 ± 9.1) and C. antarcticus (?14.7 ± 7.7) compared to field samples (?19.0 ± 9.0 and ?10.7 ± 5.2, respectively). Acclimation at +11 °C increased A. antarcticus mean SCP values (?13.0 ± 8.5) relative to field samples, whereas those of C. antarcticus again decreased (?16.7 ± 9.1). Mites acclimated under field conditions or at +11 °C selected temperatures between ?3 and +1 °C. After acclimation at ?2 °C, both species preferred +1 to +5 °C. Cryptopygus antarcticus maintained under field conditions preferred +5 to +9 °C, whereas individuals acclimated at +11 °C selected +9 to +13 °C. For A. antarcticus, thermopreference was not influenced by its cold hardened state. The distribution of field specimens was further assessed within two combined temperature and humidity gradient systems: (i) 0–3 °C/12% RH, 3–6 °C/33% RH, 6–9 °C/75% RH and 9–12 °C/100% RH and (ii) 0–3 °C/100% RH, 3–6 °C/75% RH, 6–9 °C/33% RH and 9–12 °C/12% RH. In gradient (i), C. antarcticus distributed homogeneously, but, in gradient (ii), C. antarcticus preferred 0–3 °C/100% RH. Alaskozetes antarcticus selected temperatures between 0 and +6 °C regardless of RH conditions. Cryptopygus antarcticus appears better able than A. antarcticus to opportunistically utilize developmentally favourable thermal microclimates, when moisture availability is not restricted. The distribution of A. antarcticus appears more influenced by temperature, especially during regular freeze‐thaw transitions, when this species may select low temperature microhabitats to maintain a cold‐hardened state.     

Defecation index and reproductive success of Triatoma maculata (Hemiptera: Reduviidae) under laboratory conditions

The reproductive and defecating behavior of Triatoma maculata (Erichson 1848) was studied on animals from an university culture in Venezuela. This species does not reach the importance of Rhodnius prolixus Stal 1859 as Chagas disease vector in Venezuela. This study addressed the role of defecating frequency, an index of how dangerous the animals are for the human population, and its relationship with why T. maculata is a less important vector than R. prolixus. Human blood was fed to the insects through an artificial feeding device. The 2nd and 3rd instar nymphs defecated more frequently (Id= 0.6, n=40), and our Vth instar nymphs did not complete sexual differentiation. Fertility was 55% (n=865) and fecundity 8 eggs/female/week (n=26). Egg incubation lasted 22 days (n=477). Female longevity was 51 days (n=26). Intermould time grew progressively from 35 days for 1st to 40 days for 4th instar nymphs (n=40). Mould percentage varied from 0% for Vth to 63% for 3rd instar nymphs. Mortality varied from 8% for 3rd to 100% for Vth instar nymphs. These results support evidences explaining the lesser vectorial capacity and low density of T. maculata in human domiciles, including reduced reproduction and defecation when the animal feeds on human blood.     

Developmental and reproductive patterns of Triatoma brasiliensis infected with Trypanosoma cruzi under laboratory conditions

The aim of this work was to study the interaction between Trypanosoma cruzi-1 and Triatoma brasiliensis. A group of 1st instar nymphs was initially fed on T. cruzi-infected mice and a control group was fed on uninfected mice. From the second feeding onwards, both groups were otherwise fed on non-infected mice. The resulting adults were grouped in pairs: infected male/uninfected female, uninfected male/infected female, infected male and female and uninfected male/uninfected female. The infection affected only the 1st instar nymphs, which took significantly more time to reach the 2nd instar than uninfected nymphs. The differences in the molting time between the infected and uninfected nymphs from the 2nd to the 5th instars were not statistically significant. Both groups presented similar rates of nymphal mortality and reproductive performance was not significantly affected by infection in any of the treatments.