Adult Body Size Research Articles

Research progress in fecundity study of Coleoidea (Cephalopoda)

Cephalopods are characterized by fast growth, short generation replacement and high abundance. These species live in all oceans of the world with the exception of the Black Sea, not only playing an important role in the trophic webs of the marine ecosystem but also being one of the most important fishery resources in the world. It is important to well study the fecundity of cephalopods, which can improve our understandings of their life history, and more importantly can promote to realize their population dynamics and recruitment processes. Herein, the fecundity of Coleoidea (Cephalopoda) was summarized in details, including the definitions and their determination methodologies, the values of fecundity among species, and the changeable characteristics of fecundity in relation to species body size, egg diameter and living habitats. The potential fecundity was one of the most popular approaches to determine the reproductive value, and represented the theoretical value that one species could produce during its lifecycle. Other approaches such as actual realized fecundity, effective fecundity, and relative fecundity were also used to estimate the fecundity of cephalopod species. It showed that there was species-specific fecundity for Coleoida species. The maximum potential fecundity was reported for <italic>Dosidicus gigas</italic>, and the minimum was reported for <italic>Pareledone turqueti</italic>. The fecundity of Coleoidea was generally found a linear relation to adult body size, indicating a larger body size with a higher fecundity value. At the guild level, there was a significantly negative relationship between the fecundity and egg size for both Octopoda and Teuthoidea. In contrast, there was a slightly positive relationship between the fecundity and egg size for Sepioidea. Generally, species living at lower latitudes exhibited a relatively higher fecundity, and those living at higher latitudes had a relatively lower fecundity. Meanwhile, such fecundity characteristics were also detected at the species level. Water temperature and primary production appeared to be the most important environmental factors that influenced the latitudinal trend of fecundity among the species. It is worthy to note that Coleoida species is semelparous reproduction and the fecundity is associated with the pattern and amount of energy allocation to reproduction. The reproductive investment strategy would determine the actual fecundity of a species and subsequently the biomass of recruitment, and hence studies on the potential reproductive investment will be an important area for better understanding of the fecundity characteristics of cephalopods. Increasingly, the importance of cephalopods has been recognized not only in their ecological roles as trophic indicators but also in their high abundance supporting global fisheries. Therefore, it is necessary to deeply understand the fecundity characteristics of cephalopods, which will largely increase our knowledge about their ecological roles and also assist the sustainable exploitation and the policy-making of resource assessment and management.

Comparative Reproductive Allometry of Syntopic Black-Knobbed Sawbacks (Graptemys nigrinoda) and Alabama Map Turtles (Graptemys pulchra) in the Alabama River, with Comparison to Three Congeners

In many freshwater turtle species, increasing adult female body size is accompanied by increases in both clutch size and egg size. Because clutch size and egg size represent competing sinks for the increasing abdominal space that can be devoted to reproductive potential as a female grows larger, both are hypoallometrically related to body size, i.e., each increases at less than the rate at which body size is increasing. I studied the reproductive allometry of 2 species of the map turtle and sawback genus (Emydidae: Graptemys) in syntopy in the Alabama River. Relative to congeners, Graptemys nigrinoda is a small-bodied species and Graptemys pulchra is a large-bodied species. In the study populations, adult female G. pulchra were on average 23% larger in plastron length and 125% larger in body mass and there was no overlap in size. Both species had positive but hypoallometric relationships of both clutch size and egg size with body size, a pattern reported for 3 congeners previously, thus further demonstrating the competing sinks of increases in both variables and refuting the optimal egg size hypothesis. For interspecific comparisons using analysis of covariance, there was no significant effect of species on clutch size after accounting for the effect of plastron length. The effect of species on egg width and width of the pelvic aperture was significant, with G. pulchra having relatively wider eggs and pelvic apertures, perhaps related to the more domed carapace and larger body sizes of their hatchlings. Compared with 3 congeners, the 2 Alabama River species had relatively small clutches of relatively large eggs. Latitudinal effects on reproductive output may be important in Graptemys, with more-northerly populations tending toward larger clutches of smaller eggs. There is a need to analyze more data from more populations with log-log analyses of reproductive allometry to confirm the trend. There is also a need to consider shape allometry in future analyses; in particular, the hypoallometry of both shell height and shell width relative to shell length.

Periodic Cooling during Incubation Alters the Adrenocortical Response and Posthatch Growth in Zebra Finches.

AbstractIn birds, incubation temperature is critically deterministic for a range of traits. When parents leave the nest to forage, developing embryos can be exposed to cooling events that represent thermal stress. To investigate the consequences of periodic cooling on offspring development and physiology, we exposed zebra finch embryos to cooling events throughout the incubation period. We then compared embryonic survival, egg mass change, incubation duration, posthatch growth, and adrenocortical response of these individuals with embryos reared at a constant optimal temperature of 37.4°C and embryos reared at a constant suboptimal temperature of 36.4°C, the mean incubation temperature of periodically cooled embryos. There were no differences in embryonic survival or egg mass change during incubation, but individuals exposed to periodic cooling had longer incubation periods than those from the 37.4°C treatment and shorter incubation periods than those from the 36.4°C treatment. Periodically cooled individuals showed slower posthatch growth in comparison with both constant-temperature treatments, but this did not impact adult body size. Treatment groups did not differ in their adrenocortical response, but embryos exposed to periodic cooling and a constant temperature of 37.4°C were able to habituate to repeated capture and restraint stress, while individuals exposed to the constant temperature of 36.4°C were not. These results point to the differential impacts of cooling events versus constant low temperatures during incubation on posthatch growth and physiology and may represent a way for parents to devote less energy toward incubation while still ensuring offspring success.

No rest for the weary: restricted resting behaviour of green turtles (Chelonia mydas) at a deep-neritic foraging area influences expression of life history traits

ABSTRACT For breath-holding marine animals, tradeoffs between ‘active’ and resting behaviours during periods of submergence can have consequences for acquisition and allocation of energy to vital life history requirements. In this study, we fitted 18 green turtles (Chelonia mydas) with detachable time-depth recorder (TDR) systems to obtain and analyse fine-scale dive behaviour and daily activity – with a focus on resting dive bouts – at Bahía de los Angeles (BLA), a warm-temperate foraging area in the Gulf of California, México. Our results showed that resting bout durations increased with water depths among all turtles, but patterns of resting bout durations and depths varied widely among individuals. To evaluate potential consequences to green turtles of tradeoffs between time spent ‘active’ versus resting, we also compared behavioural parameters (e.g. time spent resting, home range sizes) and life history traits (e.g. growth rates, body size at maturity) of green turtle populations from around the world, including BLA. We found that BLA green turtles spend less time resting, spend more time actively swimming and diving, occupy larger home ranges, and exhibit slower growth rates and smaller adult body sizes compared to their counterparts in other parts of the world. Unique characteristics of the BLA foraging habitat (e.g. patchy resources and temperature extremes) appear to require increased diel movements and foraging activity and decreased resting opportunities. These interactions between habitat and turtle behaviour not only influence expression of life history traits, but can also increase turtles’ exposure to human activities (e.g. vessel traffic and fisheries bycatch) as they move throughout the area.

Determining the life history strategy of the cryptobenthic reef gobies Coryphopterus hyalinus and C. personatus

Understanding the life history strategy of species can clarify their functional role, and contribution to the productivity and resilience of an ecosystem. We use otolith microstructure analysis to study the life history of 2 widespread and abundant Caribbean reef fishes, genetically identified here as the glass gobyCoryphopterus hyalinusand masked gobyC. personatus.Our analysis reveals that these species exhibit an extreme life history relative to other vertebrates due to their short lifespan, small adult body size, early maturity, and continuous growth in body length throughout reproductive age. We find that pelagic larval duration (PLD) varies widely, and average larval growth influences PLD where faster-growing larvae have shorter PLDs. We show that average daily growth substantially decreases during the settlement transition to reef habitat, approximately coinciding with reproductive maturity. Continuous somatic growth throughout reproductive age can serve to support greater fecundity in older, larger-bodied females and enhance survivorship. Several features of the ecology (i.e. broad depth range, planktivorous diet) and life history (i.e. small adult body size, quick generational turnover, short lifespan) ofC. hyalinusandC. personatusindicate that they play a key trophic role in transferring nutrients from pelagic plankton to Caribbean reef predators and the reef benthos. Our analyses highlight why life history traits related to survival, reproduction, and population dynamics can enhance our understanding of ecosystem-scale processes and functioning on coral reefs.

Land use and local environment affect macroinvertebrate metacommunity organization in Neotropical stream networks

AbstractAimChanges in land use and cover (hereafter land use) affect freshwater ecosystems at different spatial scales. We tested the effects of land use on the dispersal capacity of stream macroinvertebrates through local and regional processes.LocationIn all, 183 Brazilian headwater stream sites, located in the Neotropical Savanna with variable land use and covering a total area of 46,394 km2.TaxonStream macroinvertebratesMethodsWe used multiple regression models for distance matrices to identify the relative importance of environmental and landscape characteristics to explain community dissimilarity of stream macroinvertebrates with different mobility traits. As predictors, we calculated four distance metrics: environmental distance describing the dissimilarity in local conditions, the network distance accounting for distances across the drainage system and two distances measuring landscape resistance to dispersal (topographic and land use). We classified macroinvertebrates in dispersal groups according to their dispersal abilities (flying and drifting) and life story traits (voltinism, adult life span and body size). We tested the effects of these distances on all taxa and on the different dispersal groups, to explore whether biological traits would result in different metacommunity patterns.ResultsOur hierarchical clustering analysis identified five macroinvertebrate dispersal groups. The dispersal group 1 was mainly composed by aquatic obligate taxa, dispersal group 2 by taxa with low drift propensity, dispersal group 3 represented taxa with high directional flight capacity, dispersal group 4 included taxa with medium drift propensity and dispersal group 5 represented taxa with high drift propensity. We found that environmental distance and land use distance were the most important predictors explaining community dissimilarity for most of the dispersal groups.Main conclusionThe metacommunity patterns found in this study suggest that environmental filtering was the most important community assembly mechanism at a local scale, whereas land use could constrain dispersal at the regional scale. Understanding these processes is crucial to meet conservation and restoration goals, especially in biodiversity hotspots. Our results reinforce the importance of considering entire catchments for preserving stream health and aquatic biodiversity and indicate the need for a much more integrative research between terrestrial and aquatic ecology.

Interspecific social dominance networks reveal mechanisms promoting coexistence in sympatric charr in Hokkaido, Japan.

Coexistence of species requires equalizing mechanisms that minimize fitness differences, which are balanced by stabilizing mechanisms that enhance negative intraspecific interactions versus interspecific ones. Here, we develop a simple theoretical framework that allows measuring the relative strength of intraspecific versus interspecific competition in dominance hierarchies. We use it to evaluate mechanisms promoting coexistence between two congeneric charr that compete for foraging positions, which strongly influence density-dependent growth and survival. Agonistic interactions (n=761) among 71 Dolly Varden Salvelinus malma and whitespotted charr Salvelinus leucomaenis were measured by snorkelling in two pools in the sympatric zone of a Hokkaido stream during two summers. Interspecific dominance hierarchies, analysed using three methods, were closely correlated with fish length but the species treated each other equally. Ranks for the most dominant fish in each pool, determined directly by knockout experiments, were also virtually identical to ranks by length. Similarly, exponential random graph modelling of the social networks provided no evidence that either species was dominant over the other. Instead, larger fish were more likely to win contests, especially over fish of the next lower ranks. These results demonstrated that the two species were nearly ecological equivalents in accessing key resources in this sympatric zone. Nearly identical growth and stable densities over 4years further supported this inference, although Dolly Varden were a minority (29% of the assemblage), a sign of some fitness difference. Detailed foraging observations coupled with two concurrent studies revealed an effective stabilizing mechanism. Dolly Varden shifted to feeding directly from the benthos when drifting invertebrates declined, a behaviour enhanced by morphological character displacement, thereby partitioning food resources and enhancing intraspecific competition while avoiding agonistic encounters with whitespotted charr. The plurality of evidence indicates that fitness differences between these ecologically equivalent species are small in this local assemblage, and balanced by resource partitioning, a modest stabilizing mechanism that promotes coexistence. The theoretical framework presented here is a useful tool to evaluate the strength of interspecific versus intraspecific competition, which combined with information on trade-offs in ecological performance can contribute to a mechanistic understanding of species coexistence.

The effects of exposure to pyriproxyfen and predation on Zika virus infection and transmission in Aedes aegypti.

Zika virus (ZIKV) is an emerging mosquito-borne pathogen that can cause global public health threats. In the absence of effective antiviral medications, prevention measures rely largely on reducing the number of adult mosquito vectors by targeting juvenile stages. Despite the importance of juvenile mosquito control measures in reducing adult population size, a full understanding of the effects of these measures in determining mosquito phenotypic traits and in mosquito-arbovirus interactions is poorly understood. Pyriproxyfen is a juvenile hormone analog that primarily blocks adult emergence, but does not cause mortality in larvae. This mechanism has the potential to work in combination with other juvenile sources of mortality in nature such as predation to affect mosquito populations. Here, we experimentally evaluated the effects of juvenile exposure to pyriproxyfen and predatory mosquito Toxorhynchites rutilus on Aedes aegypti phenotypes including susceptibility to ZIKV infection and transmission. We discovered that combined effects of pyriproxyfen and Tx. rutilus led to higher inhibition of adult emergence in Ae. aegypti than observed in pyriproxyfen or Tx. rutilus treatments alone. Adult body size was larger in treatments containing Tx. rutilus and in treatments mimicking the daily mortality of predation compared to control or pyriproxyfen treatments. Susceptibility to infection with ZIKV in Ae. aegypti was reduced in predator treatment relative to those exposed to pyriproxyfen. Disseminated infection, transmission, and titers of ZIKV in Ae. aegypti were similar in all treatments relative to controls. Our data suggest that the combination of pyriproxyfen and Tx. rutilus can inhibit adult Ae. aegypti emergence but may confer a fitness advantage in survivors and does not inhibit their vector competence for ZIKV relative to controls. Understanding the ultimate consequences of juvenile mosquito control measures on subsequent adults’ ability to transmit pathogens is critical to fully understand their overall impacts.

Effects of temperature on life histories of three endangered Japanese diving beetle species

AbstractTo elucidate population‐increasing factors in the diving beetle Cybister tripunctatus lateralis (Fabricius) (Coleoptera: Dytiscidae) in Japan in recent years, life histories and oviposition patterns were compared among three endangered diving beetle species, Cybister brevis Aubé (qualified by the Japanese Red Data List as ‘near threatened’), Cybister chinensis Motschulsky (vulnerable), and C. tripunctatus lateralis (vulnerable). Oviposition in C. brevis, C. chinensis, and C. tripunctatus lateralis was observed from late April to mid‐June, from late April to early July, and from late May to mid‐August, respectively, under semi‐outdoor conditions. There were no interspecies differences in total hatchling production during the reproductive season. In rearing experiments at various temperatures (20, 23, 25, 28, and 30 °C), the mortality of C. tripunctatus lateralis larvae was higher at 20 °C, and gradually lower with increasing temperature up to 30 °C. Adult body size of females in C. tripunctatus lateralis is larger than that of males but there were no significant differences among temperatures (25–30 °C). Cybister brevis had a higher emergence rate at 23–28 °C than at 20 and 30 °C. In C. brevis, the body size of adults reared at 25 or 28 °C was significantly larger than at other temperatures. Cybister chinensis did not differ in emergence rate and adult body size among the five temperature conditions. The developmental zero (i.e., the lower developmental threshold) from the first instar to adult emergence was 11.1 °C for C. brevis, 8.7 °C for C. chinensis, and 16.8 °C for C. tripunctatus lateralis. We speculate how the influence of global warming may have a positive impact on the growth and survival of C. tripunctatus lateralis.

Comparing the Individual and Combined Effects of Ant Attendance and Wing Formation on Aphid Body Size and Reproduction

AbstractSpecies employ multiple strategies to deal with stressful environments, but these strategies often incur costs. Aphids frequently utilize multiple predator avoidance strategies, including attracting mutualist ants for protection and dispersing by producing winged forms. While both strategies can be physiologically costly, the magnitudes of these costs have not been previously compared. In this study, we experimentally manipulated ant attendance in the field and measured the individual and interactive effects of ant attendance and wing formation on body size and reproduction of the ant-tended aphid Cinara schwarzii (Wilson) (Hemiptera: Aphididae). Aphid adult body size was smaller in the presence of ants (18%), but controlling for body size, there were no differences in embryo number or size. In contrast, wing formation did not affect adult body size but strongly reduced embryo number (46%) and size (8%). Although ant attendance reduced C. schwarzii wing formation, ant attendance and wing formation acted independently on aphid body size and reproduction. For comparison, we confirmed that the manipulation of ant presence had no effect on body size or reproduction of the untended co-existing congener Cinara solitaria (Gillette and Palmer) (Hemiptera: Aphididae). Complementing our empirical study, a meta-analysis of 78 responses from 24 publications showed that wing formation consistently and significantly reduces aphid body size and reproduction (37%), while the effects of ant attendance showed a mean positive effect (9%) that did not significantly differ from zero. Together, our empirical study and meta-analysis provide strong evidence for costs of wing formation but not ant attendance for aphids.

Effects of adult body size on mating success of the black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae)

Body size is a recognised factor impacting mating success of a number of insect species. The black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), which is mass produced to convert organic waste to protein, exhibits a lekking behaviour necessary for mating. However, it is not known if adult body size impacts mating success and subsequent fertile egg production. In this study, larvae were raised at two densities to produce two size classes of adults (i.e. large and small). Hourly mating observations were recorded in the following studies: (1) homogenous populations of large or small adults; (2) 50% heterogenous populations (equal number of large males with small females and vice versa); and (3) 25% heterogenous (i.e. equal number of large and small adults for both sexes). Adult weight, morphometrics of resulting adults, total number of mating pairs and failed mating attempts, multiple matings, as well as eggs produced and associated hatch rate were recorded for each experiment. Morphometrics and weights in large adults were 21 and 50% greater than small adult males and females by size and weight, respectively. The first experiment of homogenous populations (i.e. large or small) showed no significant differences across other variables measured. However, when populations of different sized adults were mixed equally based on sex (i.e. 50% heterogenous populations), mating success increased 50 to 100% for small males with large females and large males with small females, respectively. Total number of multiple matings increased two to three times. Egg production decreased 15-20% and hatch rate declined approximately 10%. In the 25% heterogenous populations, data were more complex. Number of successful mating pairs across male size was 280% greater than in the homogenous populations. Number of failed mating attempts was also two to three times greater. Multiple matings overall were low (10%) for the homogenous and heterogenous populations. Large males demonstrated two times more aggression in general than small males in the heterogenous than the homogenous populations. Approximately 48 to 343% more eggs were produced in the 25% heterogenous population than large or small homogenous populations, respectively, while hatch rate did not differ among heterogenous and homogenous populations, with an average of 70%. However, the variability in egg hatch was forty times greater than the large homogenous and 40% greater than the small homogenous. While increased egg production is desired, high variability in egg hatch impedes fertile egg production and predictability at an industrial scale.

Early-life effects on body size in each sex interact to determine reproductive success in the burying beetle Nicrophorus vespilloides.

Early-life conditions have been shown to have a profound effect on an animal's body size and fecundity across diverse taxa. However, less is known about how early-life effects on fecundity within each sex interact to determine reproductive success. We used experiments with burying beetles Nicrophorus vespilloides to analyse this problem. The nutritional conditions experienced by burying beetles in early life are a key determinant of adult body size in both sexes, and adult body size in turn influences male reproductive tactics. In previous work, we showed that smaller males are more effective than larger males at stimulating virgin female fecundity. In this study, we manipulated male and female body size by restricting access to food in early development. We then conducted breeding assays, in which small and large females were mated sequentially with small and large males, and then allowed to raise offspring without paternal care. We tested whether large females, which are potentially more fecund, laid even more eggs when mated with small males. We found no evidence to support this prediction. Instead, we detected only a weak non-significant trend in the predicted direction and no equivalent trend in the number of larvae produced. However, we did find that larvae attained a greater mass by the end of development when their mother was large and mated with a small male first. We suggest that large females might have evolved counter-measures that prevent exploitation by small fecundity-stimulating males, including partial filial cannibalism. By eating surplus larvae during reproduction, larger females would leave more of the carrion for their offspring to consume. This could explain why their surviving larvae are able to attain a greater mass by the time they complete their development.

Age, growth and survival rate in two populations of Darevskia derjugini (Nikolsky, 1898) from different altitudes (Squamata: Sauria: Lacertidae)

Abstract We investigated age structure, age at sexual maturity, lifespan, growth and survival rate and adult life expectancy (as demographic life-history traits) as well as body size of two Darevskia derjugini (Artvin lizard) populations from different altitudes, using skeletochronology. Our findings indicated that age upon attaining sexual maturity was two or three years in the low-altitude population (Fındıklı) while it was three years in the high-altitude population (Murgul) for both sexes. The maximum longevity was seven years in the high-elevation site while it was six years in the low-elevation site. As reported for many lizards, we found a significant positive relationship between age and body size within each sex of Artvin lizard at both altitudes. High- and low-altitude populations did not differ in age structure, survival rates, adult life expectancy and body size. Rather than the effect of altitude, which is hard to compare without replication of other low and high altitude populations, the fact that these two populations have similar growth rates and the similarity of local conditions (food availability and predator density) may indicate similarity between the two regions.

The osteohistology of new remains of Pararhabdodon isonensis sheds light into the life history and paleoecology of this enigmatic European lambeosaurine dinosaur

Pararhabdodon isonensis was the first species of lambeosaurine hadrosaurid described in Europe and is one of the last non-avian dinosaurs that lived before the K-Pg extinction. Yet, its relationship with other Ibero-Armorican lambeosaurines has remained controversial due to the lack of overlapping diagnostic material among taxa. Newfound hindlimb materials reveal a unique character for the species that reinforces its distinction from other European lambeosaurines and its postulated close relationship with Tsintaosaurus spinorhinus. P. isonensis becomes restricted to the upper Maastrichtian Talarn Formation.Our osteohistological analysis indicates that Pararhabdodon isonensis probably reached adult body sizes comparable to those of other Ibero-Armorican lambeosaurines and nearing the body sizes of North American and Asian taxa. Its histomorphology indicates a relatively low growth rate, suggesting the achievement of larger body sizes over longer time periods, perhaps facilitated by a relatively low predation pressure. Unlike coeval dinosaurian clades of the Late Cretaceous European Archipelago, P. isonensis and at least some of the other Ibero-Armorican lambeosaurines that reached similarly large body sizes, like Adynomosaurus arcanus, represent exceptions to the ‘island rule’.

Adaptive differentiation of growth, energetics and behaviour between piscivore and insectivore juvenile rainbow trout along the Pace-of-Life continuum.

Adaptive trade-offs are fundamental mechanisms underlying phenotypic diversity, but the presence of generalizable patterns in multivariate adaptation and their mapping onto environmental gradients remain unclear. To understand how life history affects multivariate trait associations, we examined relationships among growth, metabolism, anatomy and behaviour in rainbow trout juveniles from piscivore versus insectivore ecotypes along an experimental gradient of food availability. We hypothesized that (a) selection for larger size in piscivorous adults would select for higher juvenile growth at the cost of lower active metabolism; (b) elevated growth of piscivores would be supported by a greater productivity of their natal stream and more proactive foraging behaviours and (c) general patterns of multivariate trait associations would match the predictions of the Pace-Of-Life Syndrome. Relative to insectivores, piscivorous fry showed a pattern of higher growth (+63%), maximum food intake (+33%), growth efficiency (+41%) and standard metabolic rate (SMR; +47%), but lower active metabolic capacity (maximum metabolic rate [MMR; -17%], aerobic scope [AS; -48%]), suggesting that faster piscivore growth is supported by greater food intake and digestive capacity but is traded-off against lower scope for active metabolism. A similar trade-off appeared among organ systems, with piscivorous fry exhibiting an 83% greater investment in average mass of organs associated with food consumption and processing (i.e. stomach and intestine), but an apparently smaller relative investment in organs involved in cardiovascular or cognitive activities (heart and brain, respectively). Higher invertebrate drift in their natal rearing habitat, quicker behavioural transition to a novel food source and lower anxiety after a frightening event in piscivorous fry suggest that faster growth requires both proactive foraging behaviours and higher prey availability in the environment. Finally, the sampling of replicate insectivore populations confirmed their lower juvenile growth (-73% on average) and reduced environmental productivity of their natal streams (-45% lower drift abundance) relative to the piscivore ecotype. Our results suggest that selection for large adult body size influences selection on high juvenile growth, high basal metabolism and proactive behaviours, and that the intense phenotypic divergence between piscivorous and insectivorous rainbow trout may be constrained by environmental productivity.

Harrison's rule scales up to entire parasite assemblages but is determined by environmental factors.

Harrison's rule states that parasite body size and the body size of their hosts tend to be positively correlated. After it was proposed a century ago, a number of studies have investigated this trend, but the support level has varied greatly between parasite/host associations. Moreover, while the rule has been tested at the individual species level, we still lack knowledge on whether Harrison's rule holds at the scale of parasite and host communities. Here, we mapped flea (parasites) and rodent (hosts) body sizes across Mongolia and asked whether Harrison's rule holds for parasite/host assemblages (i.e. whether a parasite's average body size in a locality is positively correlated with its host's average body size). In addition, we attempted to disentangle complex relationships between flea size, host size and environmental factors by testing alternative hypotheses for the determinants of fleas' body size variation. We gathered occurrence data for fleas and rodents from 2,370 sites across Mongolia, constructed incidence matrices for both taxa and calculated the average body sizes of fleas and their hosts over half-degree cells. Then, we applied a path analysis, accounting for spatial autocorrelation, trying to disentangle the drivers of the correlation between parasite and host body sizes. We found a strong positive correlation between average flea and host size across assemblages. Surprisingly though, we found that environmental factors simultaneously affected the body sizes of both fleas and hosts in the same direction, leading to a most likely deceptive correlation between parasite and host size across assemblages. We suggest that environmental factors may, to a great extent, reflect the environmental conditions inside the hosts' burrows where fleas develop and attain their adult body size, thus influencing their larval growth. Similarly, rodent body size is strongly influenced by air temperature, in the direction predicted by Bergmann's rule. If our findings are valid in other host-parasite associations, this may explain the dissenting results of both support and lack thereof for Harrison's rule.

Growth hormone and aging.

Growth hormone (GH) actions impact growth, metabolism, and body composition and have been associated with aging and longevity. Lack of GH results in slower growth, delayed maturation, and reduced body size and can lead to delayed aging, increased healthspan, and a remarkable extension of longevity. Adult body size, which is a GH-dependent trait, has a negative association with longevity in several mammalian species. Mechanistic links between GH and aging include evolutionarily conserved insulin/insulin-like growth factors and mechanistic target of rapamycin signaling pathways in accordance with long-suspected trade-offs between anabolic/growth processes and longevity. Height and the rate and regulation of GH secretion have been related to human aging, but longevity is not extended in humans with syndromes of GH deficiency or resistance. However, the risk of age-related chronic disease is reduced in individuals affected by these syndromes and various indices of increased healthspan have been reported.

Regulation of Body Size and Growth Control.

The control of body and organ growth is essential for the development of adults with proper size and proportions, which is important for survival and reproduction. In animals, adult body size is determined by the rate and duration of juvenile growth, which are influenced by the environment. In nutrient-scarce environments in which more time is needed for growth, the juvenile growth period can be extended by delaying maturation, whereas juvenile development is rapidly completed in nutrient-rich conditions. This flexibility requires the integration of environmental cues with developmental signals that govern internal checkpoints to ensure that maturation does not begin until sufficient tissue growth has occurred to reach a proper adult size. The Target of Rapamycin (TOR) pathway is the primary cell-autonomous nutrient sensor, while circulating hormones such as steroids and insulin-like growth factors are the main systemic regulators of growth and maturation in animals. We discuss recent findings in Drosophila melanogaster showing that cell-autonomous environment and growth-sensing mechanisms, involving TOR and other growth-regulatory pathways, that converge on insulin and steroid relay centers are responsible for adjusting systemic growth, and development, in response to external and internal conditions. In addition to this, proper organ growth is also monitored and coordinated with whole-body growth and the timing of maturation through modulation of steroid signaling. This coordination involves interorgan communication mediated by Drosophila insulin-like peptide 8 in response to tissue growth status. Together, these multiple nutritional and developmental cues feed into neuroendocrine hubs controlling insulin and steroid signaling, serving as checkpoints at which developmental progression toward maturation can be delayed. This review focuses on these mechanisms by which external and internal conditions can modulate developmental growth and ensure proper adult body size, and highlights the conserved architecture of this system, which has made Drosophila a prime model for understanding the coordination of growth and maturation in animals.

Transgenerational plasticity mediates temperature effects on fitness in the water fleaDaphnia magna

Phenotypic plasticity is an important way by which organisms respond to changes in their local environment, but it is not clear whether parents can buffer the negative impacts of high temperature on offspring fitness. To investigate this question, we exposed the water flea Daphnia magna Straus, 1820 and their offspring to either low (15 °C) or high (25 °C) temperature in a crossed factorial design. High parental temperature reduced the age and size at reproductive maturation and resulted in smaller mean clutch size, regardless of offspring temperature. This suggests that parents did not buffer the effects of high temperature on their offspring. However, offspring raised at high temperature that came from parents also raised at high temperature had similar adult body size and longer lifespan than offspring produced by parents exposed to low temperature. As a consequence of these apparent trade-offs, there was no detectable effect of parental temperature on offspring lifetime reproductive success. These results suggest that although transgenerational plasticity could help organisms to cope with stressful changes in their local environment, such effects might be difficult to detect in natural populations due to associated life-history trade-offs.

A Comparison of Fitness-Related Traits in the Coleopteran Parasitoid Dastarcus helophoroides (Coleoptera: Bothrideridae) Reared on Two Factitious Hosts.

The coleopteran parasitoid Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is considered an efficient preventative method against the damage caused by a large number of cerambycid pests in China and other East Asian countries. Mass rearing of this parasitoid depends on screening appropriate factitious hosts. In this paper, the fitness-related traits of this parasitic beetle were explored using pupae of the two tenebrionid beetles, Tenebrio molitor Linnaeus and Zophobas morio Fabricius (Coleoptera: Tenebrionidae) as factitious hosts. The results showed that in dual-choice trials, D. helophoroides larvae preferred to attack Z. morio pupae. In no-choice trials, D. helophoroides reared on Z. morio pupae displayed significantly higher pupation and emergence rate, longer developmental duration of larval and larval-pupal stages, larger adult body size, shorter preoviposition period, more egg masses and egg production, and higher relative expected reproduction than those reared on T. molitor pupae. These results demonstrate that Z. morio is a more suitable factitious host for mass rearing of D. helophoroides.