Experimental studies on the life cycle ofJassa falcata (Crustacea,Amphipoda)

Jassa falcata (Leach), an unselective suspension feeder, was cultivated in standing, unaerated finger bowls, feeding on a mixture ofBrachionus plicatilis, Scrippsiella faeroense, Ulva spec., and natural detritus. This amphipod can also be maintained with diets composed of dead or live material of both plant and animal origin, but an addition of living zooplankton is necessary for longterm cultivation. Starvation resistance is higher in females than in males, and it is increased by lower temperatures. The life span ofJ. falcata increases with decreasing temperature, and it is generally higher in females (maximum: 252 days at 10°C) than in males. In laboratory culture, a bimodal mortality pattern is typical with high juvenile death rates, low mortality during the reproductive phase, and again increasingly high death rates toward the end of the life cycle. Growth rate depends on temperature, sex, and individual age. The temperature dependence of growth is particularly high in males, and it is higher in adults than in juveniles. The total number of moults is lower in males (5 to 6) than in females (7 to 9). Sexual maturity is attained at moult IV to V. The average incubation time of eggs is about 9 to 16 days (highest value at 10°C). Three to 4 broods were observed, with largest numbers of offspring at 10°C.     

Moulting patterns inClethrionomys gapperi

Small northern mammals undergo regular developmental and seasonal moults. However, the moulting patterns of many small mammals are not well known. Development and subsequent moulting of the pelage was documented in adult red-backed volesClethrionomys gapperi Vigors, 1830 and their offspring in relation to age, weight, and sex. Red-backed voles exhibited 4 developmental pelages (nestling, juveniles, subadult, and adult) through diffuse, rapid hair growth. Rapid growth was associated with early moulting at the nestling, juveniles and adult stages. However, a trade-off between moulting and growth existed at the subadult stage such that delayed moulting was associated with rapid growth. Adult voles completed a unique moult progression with highly variable timing. Male and femaleC. gapperi showed no differences in pattern or locations of moulting. Variation in the number and timing of moults in small mammals may reflect differences in life-history strategies and highlights the need for a consistent mammalian pelages and moults nomenclature.     

First report on the life history of the marine amphipod Ceradocus mizani and its implication for aquaculture

The search for alternative live feed for aquaculture stocks has inspired research into marine amphipods. In this study, the life history of Ceradocus mizani was evaluated to better understand how this amphipod might be used in aquaculture as an alternative feed. The amphipods did not display copulatory behavior during the study period. The females were multivoltine and attained sexual maturity on average in 23.6 days at a mean length of 4.64 mm. The incubation period lasted 8.8 days, and the mean number of juveniles produced per brood during that incubation period was relatively low (7.58). Females produced a mean of 5.2 consecutive broods and 39.4 total juveniles over the life span. (i.e., 0.33 juveniles/day). Sex ratio was female skewed (1.55:1). Female size and the number of juveniles produced per brood were positively correlated (R² = 0.63). The mean life span for females and males was 119.4 and 91.2 days, respectively. Mean maximum length was 9.26 mm for males and 8.18 mm for females. This is the first account of the life history of C. mizani and forms the basis for future studies of this marine amphipod.     

Towards a mechanistic understanding of insect life history evolution: oxygen‐dependent induction of moulting explains moulting sizes

Moults characterise insect growth trajectories, typically following a consistent pattern known as Dyar's rule; proportional size increments remain constant across inter‐instar moults. Empirical work suggests that oxygen limitation triggers moulting. The insect respiratory system, and its oxygen supply capacity, grows primarily at moults. It is hypothesized that the oxygen demand increases with increasing body mass, eventually meeting the oxygen supply capacity at an instar‐specific critical mass where moulting is triggered. Deriving from this hypothesis, we develop a novel mathematical model for moulting and growth in insect larvae. Our mechanistic model has great success in predicting moulting sizes in four butterfly species, indirectly supporting a size‐dependent mechanism underlying moulting. The results demonstrate that an oxygen‐dependent induction of moulting mechanism would be sufficient to explain moulting sizes in the study species. Model predictions deviated slightly from Dyar's rule, the deviations being typically negligible within the present data range. The developmental decisions (e.g. moulting) made by growing larvae significantly affect age and size at maturity, which has important life history implications. The successful modelling of moulting presented here provides a novel framework for the development of realistic insect growth models, which are required for a better understanding of life history evolution.     

Number of flagellar segments and moulting in the amphipod Gammarus pulex

SUMMARY. The number of flagellar segments on the antennules of Gammarus pulex was quantitatively related to body size in animals from natural populations and to moulting and instar number of isolated animals grown from birth in the laboratory. The number of segments was 5.0 at birth increasing to means of 19–20 in females and 21–22 in males at sexual maturity or c. 5 mg wet wt reached after nine or ten moults. Addition of segments to the paired flagellae of juveniles was not regular and the number of segments cannot be used to identify particular instars of individuals or to determine their age. The mean interval (days) between moults progressively increased in the later juvenile instars and was exponentially related to moult number, age and the number of flagellar segments; the moult interval is also exponentially related to these variables in adults.     

Different paths to sexual size dimorphism in two praying mantids,Pseudomantis albofimbriata and Hierodula majuscula

Sexual size dimorphism （SSD） is widespread among diverse animal taxa and has attracted the attention of evolutionary biologists for over a century. SSD is likely to be adaptive and the result of divergent selection on different size optima for males and females, given their different roles in reproduction. The developmental trajectory leading to SSD may help us to understand how selection acts on male and female size. Here, we describe the growth and development of two Australian praying mantids, Pseudomantis albofimbriata and Hierodula majuscula including the number of moults, time to adulthood, size at each moult, and the degree of SSD. While both species exhibit the common pattern of female-biased SSD, the number of moults required for individuals to reach adulthood differed between males and females and between species. Despite their larger adult size, P. albofimbriata females require fewer moults and less time than males to reach adulthood, but are significantly larger than males from the second instar onwards. In contrast, H. majuscula males reached adulthood in fewer moults, and less time than females, however males and females did not differ in size until females went through their final moult into adulthood. H. majuscula also required more time and more moults to reach adulthood than 17. albofimbriata. We discuss these different developmental pathways in light of the existing knowledge of reproductive biology for each species. We also suggest that these differences may relate to the different phenologies that occur in strongly seasonal temperate environments compared with those in the tropics. This study provides evidence that SSD can result from two different patterns of growth and development in closely related species.     

Feeding rates of the nemertean Prosorhochmus americanus (Hoplonemertea) on two species of gammaridean amphipods

Abstract. The intertidal hoplonemertean Prosorhochmus americanus is a common inhabitant of the fouling community of rock jetties of the southeast coast of the United States. We undertook a laboratory investigation of the feeding rate of this nemertean, which is a suctorial predator of amphipod crustaceans that co‐occur in abundance in the fouling community. While submerged in water (simulating high tide), worms fed on the tube‐building amphipods Jassa falcata and Corophium cf. insidiosum at rates of 0.19 amphipods nemertean^?1 d^?1 (n=10) and 0.26 amphipods nemertean^?1 d^?1 (n=14), respectively. These predation rates were not significantly different (two‐tailed t‐test, p>0.05), and are similar to those estimated in laboratory studies of other suctorial nemerteans. Many nemerteans are typically more active at night, and indeed, adults of P. americanus consumed more individuals of J. falcata during dark periods than during light periods (χ² analysis, p<0.05). However, no difference in consumption of individuals of C. cf. insidiosum was observed in dark versus light. We attribute these contrasting results to differences in tube‐building behavior exhibited by these two species of amphipod under laboratory conditions. Our results and those of other laboratory investigations suggest that nemerteans that prey on amphipods feed at a rate of ～0.2 prey items nemertean^?1 d^?1, but under natural conditions this rate may not be obtained because of limited feeding time, longer foraging distances, and emigration of prey from regions of high nemertean activity.     

Growth and survival of neotropic cormorant (Phalacrocorax brasilianus) chicks in relation to hatching order and brood size

We investigated chick development and feeding rate in the neotropic cormorant, Phalacrocorax brasilianus, in a colony in Central Chile. The year of our study was characterized by relatively good foraging conditions. Brood sizes varied from two to five chicks, and hatching was asynchronous, with gaps of 0 to 6 days between the youngest and the oldest chick. Egg size declined over laying order in three-egg clutches, but not in four-egg clutches. Hatch weight did not vary with hatching position, irrespective of brood size. Chicks increased mass on average by 60 g/day between 8 and 20 days of age. Growth rates and survival to fledging depended on hatching position only in broods of four, where D-chicks grew slower and showed a higher pre-fledging mortality. There was a non-significant tendency that also A-, B-, and C-chicks in broods of four grew slower than in smaller broods. Average number of fledglings was 2.76. Feeding frequency decreased with chick age between the ages of 10–40 days. Four-chick broods received more feeds per day than smaller broods, leading to a similar per-chick feeding frequency across all brood sizes. D-chicks were clearly disadvantaged in growth and survival, and facultative brood reduction occurred.     

Resource partitioning in two coexisting cladocerans,Daphnia magna and Scapheloberis kingi (Anomopoda: Daphniidae), in north-eastern Algeria

Life-history traits of two coexisting cladocerans, Daphnia magna Straus and Scapheloberis kingi Sars, inhabiting a temporary pond in north-eastern Algeria were monitored in 2013 under laboratory conditions. Their life histories were compared for differences in traits such as age and size at first reproduction, size of neonates, brood size, number of broods per female, total life span and intrinsic rate of increase (r_m). Data were recorded during their entire life cycle. Daphnia magna, the larger species, could possibly be more successful in colonising temporary habitats than S. kingi because it allocates more energy to reproduction. Scapheloberis kingi, the smaller species, starts reproduction early, resulting in a smaller brood size and a shorter life span with fewer broods. Consequently, S. kingi produces a smaller number of neonates during its lifetime and has a lower r_m. In contrast, D. magna delays reproduction but produces a larger brood size and, because it is longer-lived, produces more broods and so produces a greater number of neonates and has a higher r_m over its lifetime.     

Population dynamics and feeding behavior of Triatoma brasiliensis and Triatoma pseudomaculata, main vectors of chagas disease in Northeastern Brazil

Biological parameters of Triatoma brasiliensis and T. pseudomaculata that could influence the epidemiological importance of these insects as vectors of Trypanosoma cruzi were compared. The parameters studied were incubation period, interval between hatching or moulting and first feeding, number of blood meals, development time, mortality, net reproductive rate, instantaneous daily reproductive rate, time-lapse before starting feeding, duration of feeding, blood ingestion capacity, occurrence of defecation and blood ingestion velocity. Most aspects of feeding were similar for the two species, although T. pseudomaculata had a longer life cycle than T. brasiliensis producing one and two generations per year, respectively. The two species had similar instantaneous daily rates of population growth.     

The costs of crest induction for Daphnia carinata

The effects of notonectid-induced crests on growth and reproduction, and resource allocation to crest construction, moult losses and eggs of Daphnia carinata were measured. An attempt was made to elucidate the mechanisms of physiological costs of crest induction for this species. The crested morph of d. carinata reached a significantly larger size than the uncrested form. Reproductive output was similar in early instars, but the crested morph produced more eggs in latter broods. Instar duration was longer for the crested morph and age at first reproduction was delayed. Survival was also lower in this form. Crest construction required significant resources (equivalent to 60 eggs over a life time) but evidence is presented that these resources were obtained primarily by re-allocation of available material rather than collection of extra resources. The crested morph allocated significantly more resources to moulting than its uncrested counter-parts. The uncrested morph produced large eggs in early instars and progressively smaller ones in later instars. The crested morph produced only small eggs. The hypothesis is presented that the crest-induction strategy of D. carinata involves at least two separate sets of responses, each with its own costs and trade-offs. The first response is production of the crest. The cost of crest production is an increased cost of moulting. D. carinata off sets this cost by increasing instar duration and thus age at reproduction. The second response is increased size. D. carinata achieves this by reducing the fraction of available resources allocated to reproduction. The cost is lower reproductive output.     

A comparison of life‐history and parental care in temperate and tropical wrens

Comparing closely related species that live in different environments is a powerful way to understand selective pressures that influence life‐history evolution. We examined a suite of life‐history traits and parental care in neotropical buff‐breasted wrens Cantorchilus leucotis and north‐temperate Carolina wrens Thryothorus ludovicianus (Family Troglodytidae), to test hypotheses about life‐history evolution. As expected, buff‐breasted wrens exhibited smaller clutch sizes and higher annual adult survival than Carolina wrens. We found minimal support for the nest predation hypothesis, as nest survival and age‐corrected provisioning rates to whole broods were similar between species, and number of breeding attempts and breeding season length were greater in temperate wrens. Critical predictions of the food limitation hypothesis were not supported; in particular age‐corrected provisioning rates per nestling were higher in the tropical than temperate species. The adult survival and offspring quality hypothesis garnered the most support, as buff‐breasted wrens exhibited greater age‐corrected provisioning rates per nestling, a longer nestling period, longer re‐nesting intervals following nest success, and lower annual fecundity than Carolina wrens. Despite similarly prolonged breeding seasons, reproductive strategies differ between species with buff‐breasted wrens investing considerably in single broods to optimize first‐year survival and Carolina wrens investing in multiple small broods to optimize annual fecundity.     

Cumulative effects matter: multi‐brood responses of Daphnia to hypoxia

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Non‐moulted primary coverts correlate with rapid primary moulting

Time constraint is a main factor which affects the moult strategies in passerines, mainly during the first year of life. The variability of moult strategies between species is associated with the extent of the moult. In the first year of life, the extent of the moult is highly variable between species and individuals. In most passerine species, juveniles only renew some of their feathers, but the factors that govern which feathers are renewed and which are retained have been largely overlooked. Here we examine the common pattern of non‐moulted primary coverts (PC) in passerines during the first‐year moult cycle (post‐juvenile and first‐year pre‐breeding moults). On the interspecific level we found that among 63 species of passerines, PCs are the least commonly moulted feather tract. For five species (Hirundo rustica, Pycnonotus xanthopygos, Prinia gracilis, Acrocephalus stentoreus and Passer moabiticus) which perform a complete post‐juvenile moult, we found that the PC moult occurs over a longer period than greater coverts (GCs) and is sequential (non‐simultaneous). At the intraspecific level, we found that the main difference between a partial and complete moult in Prinia gracilis is the moulting or non‐moulting of the PCs. We also demonstrate that for Prinia gracilis 1) juveniles which do not moult their PCs, moult their primaries at a higher speed than those which moult their PCs and 2) area/mass ratio of PCs is lower than of GCs. These two findings may explain why many passerines skip PC renewal during the first year of life. Because the PC moult lasts a long time, forgoing this moult enables long term resource savings that allow for dealing with time constraints. Our results highlight the adaptive advantages of non‐moulted PCs in cases of time constraints.     

Laboratory observations of moulting,growth and maturation in Antarctic krill (Euphausia superba Dana)

Summary Observations of intermoult period, growth and maturation were made on krill which were transported from Antarctic waters and maintained in the laboratory in Australia over a three year period. The mean intermoult period (IP) for each of 10 specimens, with initial body lengths of 24.7=46.8 mm, kept at -0.5° C varied from 22.0 to 29.8 days (overall mean = 26.6 days). These measurements of IP are significantly longer than those obtained in some previous studies. Differences in experimental temperatures, light, body sizes and growth patterns of the specimens between studies are unlikely to be causes of these dissimilar results. The pattern of changes in body length (BL) varies from one individual to the next. The greatest increase in BL over a series of 4–5 moults ranged from 0.024 to 0.070 mm/day, which is equivalent to 0.0020 to 0.0086/day in body weight, assuming exponential growth. This maximum growth rate is about half the rate predicted from the growth scheme of Mauchline (1980) for wild krill. Comparison of growth data for other euphausiids suggests that Mauchline's scheme produces anomalous growth rate. The slower growth rate observed in the present study would extend the estimated life span of krill from 3–4 years, as calculated by Mauchline (1980), to 4–7 years. If krill undergo body shrinkage during the Antarctic winter the estimated life span might be even longer. Examination of the external sexual characters of moults showed both progression and regression of maturity stage in association with changes in BL.     

Population studies on the Amphipoda of Mazoma Lagoon (Greece)

The life cycles of four amphipod species—Gammarus insensibilis, Dexamine spinosa, Microdeutopus gryllotalpa andCorophium insidiosum—were studied in the brackish-water lagoon Mazoma of the Amvrakikos Gulf, Ionian Sea.G. insensibilis has an annual life cycle with limited recruitment over the year and maximum reproductive activity in the winter months.D. spinosa exhibits continuous recruitment in the lagoon with a maximum in summer. Both species produce a single brood per female per yer. Continuous recruitment was observed during the summer months forM. gryllotalpa andC. insidiosum, and multiple breeding per female per year. Sex ratios varied considerably over the year, with a persisting preponderance of the females.     

The timing of breeding and wing-moult of four African Sturnidae

Wing-moult of the Cape Glossy Starling, Red-winged Starling, Pale-winged Starling and Pied Starling was examined primarily from specimens in southern African museums. Breeding data were obtained from nest record cards.
The Cape Glossy Starling breeds from October to March, with the moult period from December to May. There is no evidence of moult-breeding overlap in individual birds. The Red-winged Starling breeds from September to March, while the moult takes place between November and April, overlapping with the second broods. The Pale-winged Starling breeds from October to April and moults between November and May. The Pied Starling moults between November and April, while breeding varies regionally, occurring concurrently with moulting in some areas.     

Survival for specific life intervals of smallmouth bass, Micropterus dolomieu, during parental care

We tested whether daily mortality rates (DMR) of smallmouth bass offspring were influenced by life interval, offspring density and growth, parental male attributes, and selected mortality factors during parental care in a regulated Virginia stream. Mortality averaged 9.5% per day (range 5.2–13.9%) and 94.1% total (range 80.9–99.5%) from egg deposition to the juvenile period (29–36 d) for individual broods. Offspring losses were primarily attributed to fungus (Saprolegnia parasitica) infection of eggs and to American eel, Anguilla rostrata, predation. DMR were significantly higher for the interval from swim-up of larvae to metamorphosis relative to earlier and later intervals. There was no significant autocorrelation of DMR among life intervals for individual broods, indicating that relative mortality rates were inconsistent among broods through time. DMR were also uncorrelated with the number of offspring per brood, offspring growth rates, and parental male attributes, except during egg and embryo intervals. Daily egg mortality was negatively related to male size and positively related to the number of eggs per nest, suggesting that density-dependent egg mortality may have been partially offset in nests of larger males. Larger males received more eggs, tended to maintain larger broods throughout parental care, and contributed a high proportion of the total number of juveniles reared. This revised version was published online in August 2006 with corrections to the Cover Date.     

Life history changes in Trogoderma variabile and T. inclusum due to mating delay with implications for mating disruption as a management tactic

Controlling postharvest pest species is a costly process with insecticide resistance and species‐specific control requiring multiple tactics. Mating disruption (MD) can be used to both decrease a female's access to males and delay timing of mating and decreases overall mating success in a population and population growth rate. Development of new commercially available MD products requires an understanding of life history parameters associated with mating delay. These can provide information for targeting proportions of reproducing individuals using MD. After delaying mating for females of two closely related beetle species, Trogoderma variabile and T. inclusum, we surveyed survivorship, number of eggs laid, and number of progeny emerged. With increases in mating age, total number of eggs laid and total number of progeny emerged significantly declined over time. T. inclusum typically had greater numbers of eggs laid and progeny emerged compared to T. variabile as female age at mating increased, suggesting that T. inclusum may be more resistant to long‐term delays in mating. Life span showed an increase as mating age increased but life span significantly decreased almost immediately following mating. Simulations depicting multiple distributions of mating within a population suggest that in a closed population, high levels of mating delay significantly reduced reproductive growth rates. Although reproductive growth rates were decreased with increased mating age, they are still large enough to maintain populations. This study highlights the differences in life history between two closely related species, suggesting that T. inclusum outperforms T. variabile over the course of a life span, but T. variabile has better reproductive capabilities early in life. MD may also be a viable component of a pest management system for these two species as it significantly decreased overall reproductive output and population growth.     

Mate guarding behaviour in the supralittoral isopod,Ligia dentipes (Oniscidea) from the Andaman and Nicobar Islands

Precopulatory mate guarding is a characteristic feature in the mating behaviour of many Malacostraca, and a necessary prerequisite for those species in which female receptivity for males is restricted to a short period of time after the pubertal/reproductive moult. This study deals with the pre-mate guarding behaviour of the semi-terrestrial isopod Ligia dentipes living in the crevices of coral boulders and rocks in the supralittoral region of the Andaman Islands. As in other isopods, moulting in L. dentipes is biphasic, in which the posterior body part invariably moults first. The guarding male aids the female partner in the removal of the moulted exoskeleton. Mating occurs immediately after the posterior body exuviates. The male leaves the female after copulation and goes in search of another receptive female, demonstrating a polygamous mating system in these isopods. The mated females also re-mate with several other males without mate guarding. Females that had mated several times produced more young, compared to females mated only once in the laboratory. Female receptivity ceases following moulting of the anterior half. Intrasexual encounters among males lead to the large males acquiring receptive females. This study reveals interesting deviations from the general pattern of mate guarding already reported in other isopods and decapods. The evolutionary and ecological significances of mate guarding, intrasexual and intersexual conflicts, found in these semi-terrestrial isopods, are discussed.