Larger Brood Sizes Research Articles

Potential drivers of differences in breeding phenology as a component of life history strategies among coexisting species

Abstract Breeding phenology can have strong demographic consequences. Yet, the reasons why coexisting animal species differ in breeding phenology have received little attention. We tested selection pressures that underlie life history variation, such as age‐specific mortality, diet, and body size to explain breeding phenology of 16 coexisting songbird species in arid shrubland in South Africa. The average start and end dates for the earliest and latest species differed by 1.5 months, with a gradient among remaining species. Nest predation risk generally increased through the season, although species differed in seasonal patterns. Species with lower annual adult mortality, greater seasonal increases in nest predation, and greater nest predation rates had earlier start and stop dates, thereby reducing demographic risks. Species with higher adult mortality had larger brood sizes that require more food and they bred later when food was more abundant. Evolved timing of breeding thereby reflected risk management and food availability related to longevity and brood size. These factors may place unrecognized constraints on within‐species responses to climate change. Given the importance of phenology for fitness, phenology should be integrated as a core life history trait in future theory, and evolutionary constraints need to be considered in responses to climate change. Read the free Plain Language Summary for this article on the Journal blog.

Early-life environmental effects on mitochondrial aerobic metabolism: a brood size manipulation in wild great tits.

In avian species, the number of chicks in the nest and subsequent sibling competition for food are major components of the offspring's early-life environment. A large brood size is known to affect chick's growth, leading in some cases to long-lasting effects for the offspring, such as a decrease in size at fledgling and in survival after fledging. An important pathway underlying different growth patterns could be the variation in offspring mitochondrial metabolism through its central role in converting energy. Here, we performed a brood size manipulation in great tits (Parus major) to unravel its impact on offspring's mitochondrial metabolism and reactive oxygen species (ROS) production in red blood cells. We investigated the effects of brood size on chicks' growth and survival, and tested for long-lasting effects on juvenile mitochondrial metabolism and phenotype. As expected, chicks raised in reduced broods had a higher body mass compared to enlarged and control groups. However, mitochondrial metabolism and ROS production were not significantly affected by the treatment either at chick or juvenile stages. Interestingly, chicks raised in very small broods were smaller in size and had higher mitochondrial metabolic rates. The nest of rearing had a significant effect on nestling mitochondrial metabolism. The contribution of the rearing environment in determining offspring mitochondrial metabolism emphasizes the plasticity of mitochondrial metabolism in regards to the nest environment. This study opens new avenues regarding the implication of postnatal environmental conditions in shaping the offspring's early-life mitochondrial metabolism.

C22 disrupts embryogenesis and extends C. elegans lifespan.

Caenorhabditis elegans is an instrumental model in aging research due to its large brood size, short lifespan, and malleable genetics. However, maintaining a synchronous nematode population for longevity studies is challenging and time consuming due to their quick rate of development and reproduction. Multiple methods are employed in the field, ranging from worm strains with temperature dependent sterility to DNA replication inhibitors such as 5'-fluorodeoxyuridine (FUdR). In this study, we characterize a small molecule (C22) that impairs eggshell integrity and disrupts early embryogenesis to determine its applicability as a potential FUdR alternative. We find that C22 prevents egg hatching in a concentration dependent manner. However, it extends the lifespan of wild type worms and can induce FMO-2, a longevity regulating enzyme downstream of dietary restriction. Our results suggest that C22 is unlikely to be widely useful as an alternative to FUdR but its mechanism for lifespan extension may be worth further investigation.

Age, growth and maturity of the yellow stingray (Urobatis jamaicensis), a biannually reproductive tropical batoid.

Urobatis jamaicensis is a coastal batoid species affected by habitat loss and small-scale exploitation from fisheries and the aquarium trade, yet the life-history information available is limited. This is the first study to assess the vertebral centra from 195 stingrays to estimate age and growth patterns, and compare them with the biannual reproductive pattern previously reported for this species. Age-at-size data were compared using five different growth models and found a two-parameter von Bertalanffy growth function (VBGF), the Gompertz model and a modified VBGF fit best for males, females and sexes combined, respectively. Maturity was achieved before 1 year. However, growth did not cease with the onset of maturity, but instead slowed down. Results from marginal increment analysis and edge analysis indicated a nonannual somatic growth pattern with influences from the biannual reproduction cycle where peaks in resource allocation may be focused on ovulation rather than growth during March when larger brood sizes are present, while resources may be allocated more towards growth during August and September when brood sizes are generally smaller. These results may be used as a proxy for species with similar reproductive patterns or for those that lack annual or seasonal growth patterns.

Parent-offspring cannibalism throughout the animal kingdom: a review of adaptive hypotheses.

Parents that kill and consume their offspring often appear to be acting against their own reproductive interests. Yet parent-offspring cannibalism is common and taxonomically widespread across the animal kingdom. In this review, I provide an overview of our current understanding of parent-offspring cannibalism, which has seen a proliferation in adaptive hypotheses over the past 20 years for why parents consume their own young. I review over four decades of research into this perplexing behaviour, drawing from work conducted on fishes, reptiles, insects, birds, and mammals among other taxa. Many factors have been hypothesised to explain parent-offspring cannibalism in nature, including poor parental energy reserves, small or large brood sizes, low or uncertain parentage, and high brood densities, and additional factors are still being uncovered. Parent-offspring cannibalism does not appear to have a single predominant explanation; rather, the factor, or set of factors, that govern its expression is largely taxon specific. Parents may either consume all offspring under their care (full-brood cannibalism) or consume a fraction of their offspring (partial brood cannibalism). These forms of cannibalism are thought to provide adaptive benefits to cannibals under a range of circumstances, primarily by allowing parents to allocate parental efforts more optimally - energy from eating (some of) one's current offspring can be redirected to other offspring, or to parental growth, survival, and ultimately to other future reproductive endeavours. Thus, parent-offspring cannibalism is a phenotypically plastic trait that responds to changing environmental, social, and physiological conditions. The expression of parent-offspring cannibalism in any given system is intimately linked to the reproductive value of current young relative to parents' expectations for future reproduction, and also to whether parental care is predominantly depreciable or non-depreciable. Furthermore, parent-offspring cannibalism has the potential to generate conflict between the sexes, and I briefly discuss some consequences of this conflict on patterns of mate choice. Finally, there still remain many aspects of this behaviour where our understanding is poor, and I highlight these topics to help guide future research.

Sex allocation and field population sex ratio of Apanteles taragamae Viereck (Hymenoptera: Braconidae), a larval parasitoid of the cucumber moth Diaphania indica Saunders (Lepidoptera: Crambidae)

Abstract Sex ratio is one of the most important biological characteristics of arthropods. In a parasitoid population, sex ratio can influence the suppression of host populations or the stability of host–parasitoid interactions in the field. In this study, a survey was carried out to determine the sex allocation through the sequence of male/female adult emergence and calculate the sex ratio of selected populations of Apanteles taragamae in their natural habitat. Assessment of sex ratio at the population and individual level (brood size per female) was examined. We found no difference in the likelihood that either sex would emerge before the other. Observations of sex ratio at the population and individual level reveal a females biased sex ratio. Analysis of the relationship between brood size and sex ratio of A. taragamae shows that brood size may influence the proportion of male to female offspring yielded. A male-biased sex ratio tends to be found in smaller brood size. However, sex ratio is shifted to female biased in larger brood size.

Natural variation in reproductive timing and X-chromosome nondisjunction in Caenorhabditis elegans.

Caenorhabditis elegans hermaphrodites first produce a limited number of sperm cells, before their germline switches to oogenesis. Production of progeny then ensues until sperm is depleted. Male production in the self-progeny of hermaphrodites occurs following X-chromosome nondisjunction during gametogenesis, and in the reference strain increases with age of the hermaphrodite parent. To enhance our understanding of the reproductive timecourse in C. elegans, we measured and compared progeny production and male proportion during the early and late reproductive periods of hermaphrodites for 96 wild C. elegans strains. We found that the two traits exhibited natural phenotypic variation with few outliers and a similar reproductive timing pattern as previous reports. Progeny number and male proportion were not correlated in the wild strains, implying that wild strains with a large brood size did not produce males at a higher rate. We also identified loci and candidate genetic variants significantly associated with male-production rate in the late and total reproductive periods. Our results provide an insight into life-history traits in wild C. elegans strains.

Breeding dispersal in a resident boreal passerine can lead to short‐ and long‐term fitness benefits

AbstractWhether an individual disperses or remains site‐faithful between breeding seasons can have important impacts on individual fitness and population dynamics. While several studies have identified factors influencing the probability of breeding dispersal, the consequences of dispersal are much less certain, particularly over an individual’s lifetime. Here, we use 81 cases (13 paired and 55 single dispersals) of breeding dispersal across 55 yr of breeding and re‐sighting data from an individually marked population of Canada jays (Perisoreus canadensis) at the southern edge of their range in Algonquin Provincial Park, Ontario to determine both the short‐ (year after dispersal) and long‐term (lifetime) consequences of breeding dispersal. In the year following dispersal, adults had larger brood sizes and higher nest success compared to the year prior to dispersal. However, when adults dispersed during the fall/winter, they had significantly later lay dates and lower rates of nest success than adults that dispersed during the summer. Additionally, most breeders dispersed to territories of higher quality and individuals that dispersed to a territory of lesser quality experienced lower rates of nest success. Importantly, individuals that dispersed at least once in their lifetime produced an average of 2.7 more young and recruited an average of 0.9 more juveniles into the population compared to individuals that remained site‐faithful. Our study provides rare evidence of both the short‐ and long‐term benefits of breeding dispersal in Canada jays and demonstrates how the timing of dispersal can also have consequences for individual reproductive performance.

Weather conditions explain reproductive success and advancement of the breeding season in Western Capercaillie (Tetrao urogallus)

Climate change and associated changes in weather patterns have globally widespread effects on natural systems. Shifts in phenology can affect the reproductive success of birds by causing a mismatch between the onset of breeding and favourable conditions for reproduction, such as a peak in food availability. Weather conditions and their changes have also long been discussed as affecting the reproductive success of grouse (Tetraoninae) and contributing to rapid declines in many central European populations. We monitored the reproductive success of Western Capercaillie Tetrao urogallus in the Black Forest, Germany, over a 14‐year period to study how weather conditions correlated to reproductive success and to assess whether changing environmental conditions were related to a seasonal shift in reproduction. We observed a temporal shift in peak lekking activity from late to mid‐April, which corresponds to an advance of 0.65 days/year. Furthermore, we show that warm conditions during the reproductive season were positively associated with reproductive success (i.e. larger brood size, more hens with chicks and more chicks per hen) and that precipitation volume during the early weeks after hatching was negatively correlated with brood size. Precipitation before copulation (i.e. peak of lekking) affected the proportion of hens with chicks and the number of chicks per hen. Sex ratio in broods was also affected by weather conditions, with more female than male chicks in years with low temperatures and high precipitation. By analysing spring weather predictions for the period 2020–2039, we found that weather conditions during the reproductive period remained constant when assuming a continued advancement of reproduction onset, although annual variation was high. We show the importance of weather conditions in influencing Western Capercaillie reproductive success. Western Capercaillie in the Black Forest seem to adjust the timing of reproduction according to changes in weather conditions, but this advancement is unlikely to be limitless, making the future impact of climate change on the species uncertain.

A new polychelidan lobster preserved with its eggs in a 165\u2009Ma nodule

Crustacean eggs are rare in the fossil record. Here we report the exquisite preservation of a fossil polychelidan embedded within an unbroken nodule from the Middle Jurassic La Voulte-sur-Rhône Lagerstätte (France) and found with hundreds of eggs attached to the pleon. This specimen belongs to a new species, Palaeopolycheles nantosueltae sp. nov. and offers unique clues to discuss the evolution of brooding behaviour in polychelidan lobsters. In contrast to their development, which now relies on a long-lived planktic larval stage that probably did not exist in the early evolutionary steps of the group, the brood size of polychelidan lobsters seems to have remained unchanged and comparatively small since the Jurassic. This finding is at odds with reproductive strategies in other lobster groups, in which a long-lived planktic larval stage is associated with a large brood size.

Developmental conditions modulate DNA methylation at the glucocorticoid receptor gene with cascading effects on expression and corticosterone levels in zebra finches

Developmental conditions can impact the adult phenotype via epigenetic changes that modulate gene expression. In mammals, methylation of the glucocorticoid receptor gene Nr3c1 has been implicated as mediator of long-term effects of developmental conditions, but this evidence is limited to humans and rodents, and few studies have simultaneously tested for associations between DNA methylation, gene expression and phenotype. Adverse environmental conditions during early life (large natal brood size) or adulthood (high foraging costs) exert multiple long-term phenotypic effects in zebra finches, and we here test for effects of these manipulations on DNA methylation and expression of the Nr3c1 gene in blood. Having been reared in a large brood induced higher DNA methylation of the Nr3c1 regulatory region in adulthood, and this effect persisted over years. Nr3c1 expression was negatively correlated with methylation at 2 out of 8 CpG sites, and was lower in hard foraging conditions, despite foraging conditions having no effect on Nr3c1 methylation at our target region. Nr3c1 expression also correlated with glucocorticoid traits: higher expression level was associated with lower plasma baseline corticosterone concentrations and enhanced corticosterone reactivity. Our results suggest that methylation of the Nr3c1 regulatory region can contribute to the mechanisms underlying the emergence of long-term effects of developmental conditions in birds, but in our system current adversity dominated over early life experiences with respect to receptor expression.

Ecological surveys on the parthenogenetic Artemia populations in the hypersaline lakes of Anatolia, Turkey

The objective of this study is to provide information on the parthenogenetic Artemia populations in some hypersaline lakes of Anatolia (Tuz, Bolluk, Tersakan, and Acıgöl). Sampling studies were performed for abiotic factors and population parameters between November 2009 and October 2010. During the survey we focused on the local Artemia populations to investigate population dynamics, reproduction, brood size, and cyst and naupliar biometrics. Generally, the Artemia habitats in Anatolia were relatively shallow, and thus they were subject to major seasonal fluctuations. Dramatic declines in population size in Tuz and Acıgöl Lakes were found during this study. All Artemia populations were parthenogenetic and brood sizes of females showed significant differences among the populations (P < 0.05). The largest brood size was observed in the Acıgöl population and it may be concluded that local conditions for reproductive success were more adequate in this population. Substantial differences among populations were revealed during the studies on cyst and naupliar biometry. Cyst diameter mean values ranged from 231.8 to 266.9 µm. The cyst diameters for the Acıgöl population are determined as the smallest in these populations and among the smallest values recorded in parthenogenetic populations. The total length of newly hatched nauplii ranged from 484 to 512 µm for these populations.

Cannibalism of young is related to low paternity and nest take-overs in an intertidal fish

Parental care is costly, and theory suggests that caregivers should reduce parental investment or even stop caring altogether when the costs of caring are too high or the benefits too low. Brood cannibalism is one tactic by which parents can divert investment away from current offspring and towards potentially higher-quality future offspring, but the various selective factors underlying partial brood cannibalism and their relative importance remain poorly understood. Here we used the plainfin midshipman fish, Porichthys notatus, to concurrently examine three hypotheses for partial brood cannibalism and test whether cannibalism increases when (1) parental body condition is low, (2) brood sizes are large and/or (3) brood paternity is low. To investigate these predictions, we combine multiyear, multisite field data with genetic paternity testing and show that partial brood cannibalism is not related to low parental body condition or to large brood sizes, but rather is linked to low paternity. In particular, males that had taken over nests from other males, and were thus unrelated to the broods present in the new nests, consumed the largest number of young (∼15 or more eaten at a time). Our data also suggest that the consumption of only a few young (∼1–2 at a time) appears to be governed by other factors that are not clearly related to paternity. Overall, we highlight the utility of concurrently testing multiple hypotheses for partial brood cannibalism within the same system to better understand this otherwise puzzling behaviour.

Coupling lifespan and aging? The age at onset of body mass decline associates positively with sex-specific lifespan but negatively with environment-specific lifespan.

Whether lifespan scales to age-associated changes in health and disease is an urgent question in societies with increasing lifespan. Body mass is associated with organismal functioning in many species, and often changes with age. We here tested in zebra finches whether two factors that decreased lifespan, sex and poor environmental quality, accelerated the onset of body mass declines. We subjected 597 birds for nine years to experimentally manipulated foraging costs (harsh = H, benign = B) during development (small vs large brood size) and in adulthood (easy vs hard foraging conditions) in a 2 × 2 design. This yielded four treatment combinations (HH, HB, BH, BB) for each sex. Harsh environments during development and in adulthood decreased average body mass additively. The body mass aging trajectory showed a short steep increase in early adulthood, followed by a plateau and then a decline after 5 years. This decline occurred in all groups except for HB females, which gained mass until death. Surprisingly, the onset of body mass decline was earlier in experimental groups with a longer lifespan. In contrast, the onset of body mass decline was one year earlier in females, which lived two months (4%) shorter than males. Thus, the onset of body mass aging associated positively with the sex-specific differences in lifespan, but negatively with the environmental modulation of lifespan. Thus, body mass aging trajectories did not generally scale to lifespan, and we discuss the possible causes and implications of this finding.

Caenorhabditis elegans and its applicability to studies on restless legs syndrome.

Restless legs syndrome (RLS) is a common neurological disorder in the United States. This disorder is characterized by an irresistible urge to move the legs, although the symptoms vary in a wide range. The pathobiology of RLS has been linked to iron (Fe) deficiency and dopaminergic (DAergic) dysfunction. Several genetic factors have been reported to increase the risk of RLS. Caenorhabditis elegans (C. elegans) is a well-established animal model with a fully sequenced genome, which is highly conserved with mammals. Given the detailed knowledge of its genomic architecture, ease of genetic manipulation and conserved biosynthetic and metabolic pathways, as well as its small size, ease of maintenance, speedy generation time and large brood size, C. elegans provides numerous advantages in studying RLS-associated gene-environment interactions. Here we will review current knowledge about RLS symptoms, pathology and treatments, and discuss the application of C. elegans in RLS study, including the worm homologous genes and methods that could be performed to advance the pathophysiology RLS.

Caenorhabditis elegans as a Model Host to Monitor the Candida Infection Processes.

C. elegans has several advantages as an experimental host for the study of infectious diseases. Worms are easily maintained and propagated on bacterial lawns. The worms can be frozen for long term storage and still maintain viability years later. Their short generation time and large brood size of thousands of worms grown on a single petri dish, makes it relatively easy to maintain at a low cost. The typical wild type adult worm grows to approximately 1.5 mm in length and are transparent, allowing for the identification of several internal organs using an affordable dissecting microscope. A large collection of loss of function mutant strains are readily available from the C. elegans genetic stock center, making targeted genetic studies in the nematode possible. Here we describe ways in which this facile model host has been used to study Candida albicans, an opportunistic fungal pathogen that poses a serious public health threat.

Seasonal change in sexual differences in nestling size and survival: a framework to evaluate sex-dependent environmental sensitivity in the wild

BackgroundSexual size dimorphism (SSD) occurs in a wide range of species in birds and other animals, but the magnitude of SSD often varies with environmental conditions. In general, in the developmental stages, the larger sex is more vulnerable to adverse environmental conditions because the larger sex requires more energy than the smaller sex. However, this may not hold true for birds with large brood sizes; the larger sex can acquire more food by suppressing the smaller sex. In addition, most previous studies have been experimental, such as by manipulating clutch size and ectoparasites, which may not reflect natural conditions.MethodsIn the present study, we propose a general framework to assess sexual differences in environmental sensitivity in natural populations. Because environmental conditions change throughout the breeding season, seasonal changes of nestling SSD and sex ratio should reflect sexual differences in environmental sensitivity. We applied this approach to a large dataset (1555 nestlings over 5 years) of Japanese Tits (Parus minor). In this population, the male nestling is generally larger than the female (5% SSD in body weight).ResultsWe found that the magnitude of SSD (weight, tarsus, wing) and fledgling sex ratio increased both in the beginning and the end of the breeding season.ConclusionOur study suggested that female nestlings are more valuable to poor environmental conditions in the relatively fecund species. This study underscores the importance of brood size on sexual differences in environmental stochasticity and our framework encourages comparative analysis among different bird species.

Carry-over effects of brood size on morphology, reproduction, and lifespan in barn swallows

Early life ecological conditions have well-documented short-term effects on offspring phenotype and survival, but the extent to which these effect carry-over into adulthood is much less known. Yet, unveiling such carry-over effects is essential to understand the evolution of parental life-history strategies. In altricial birds, the number of brood mates can affect competition regime and other nest ecological conditions, whose effects may be at least partly expressed in adulthood. We either increased or decreased the size of barn swallow (Hirundo rustica) broods and analyzed the consequences of brood size manipulation on morphological feather traits, breeding performance, and lifespan of the offspring when adult. Upon recruitment (age 1 year), individuals from enlarged broods had shorter wings, later reproduction, and lower breeding output than those from reduced broods. The negative effect of brood enlargement on wing length persisted at age 2 years. Recruits from enlarged broods had longer lifespan but the proportion of nestlings that were recruited tended to be smaller for enlarged compared to reduced broods. Hence, large brood size had negative phenotypic effects in adulthood. Our results also suggest that stronger viability selection on offspring from enlarged broods results in differential survival of highly viable offspring that express longer life expectancy when adult and/or that smaller reproductive effort of 1-year-old offspring from enlarged broods boosts their life expectancy, potentially compensating for reduced annual fecundity. Number of brood mates can thus have carry-over effects on fitness components, including lifespan, which should be incorporated in the analysis of complex reproductive trade-offs. Ecological conditions in early life can affect survival and physical conditions but the extent to which these effects extend into adulthood is largely unknown. In this experiment, we altered the size of barn swallow broods and monitored the consequences of the change in competition regime in the brood of rearing in adulthood. When adult, individuals that had been reared in an enlarged brood had shorter wings and decreased breeding success. However, individuals from enlarged broods lived longer, possibly because only high-quality individuals from such broods survived through the first year of life. Thus, rearing conditions have important long-term effects, implying that parents have to optimize the number of offspring they decide to produce.

Leucocyte Profiles and Family Size in Fledgling Greylag Geese (Anser Anser)

In precocial species, large brood sizes are usually considered as beneficial and individuals in larger broods grow faster and are more dominant compared to individuals in small broods. However, little is known whether family size also beneficially affects the offspring's physiology. In the present study, we investigated whether leucocyte profiles in fledgling Greylag Geese ( Anser anser) are affected by (1) family size, (2) individual characteristics, i.e. age, body condition or sex, or (3) characteristics of the parents, i.e. previous reproductive success. From spring 2013 to autumn 2015, we collected blood samples from 100 juvenile Greylag Geese from 20 different pairs. From these samples we determined the absolute leucocyte number, an individual's differential blood cells count and an individual's haematocrit (HCT). The number of fledglings in a family and therefore the number of siblings a focal individual had, was positively related to the percentage of basophils, negatively to the heterophils/lymphocytes ratio (H/L), and tended to be negatively related to the percentage of monocytes and eosinophils in a sample. H/L ratio was negatively related to age in days and tended to be negatively related to body condition, whereas the percentage of basophils tended to be positively related to it. Absolute leucocyte number did not differ between individuals depending on family size. However, composition of different leucocyte types (basophils, eosinophils, H/L ratio) was modulated mostly by the social environment (family size) and not by the characteristics of the individual or the parents. In conclusion, even though we did not find clear evidence of a positive health effect, i.e. a better immune system, in fledgling Greylag Geese of large versus small families, our results suggest that family size modulates different components of the immune system hinting at its stress-reducing effect.

Bacterial traits and quality contribute to the diet choice and survival of bacterial-feeding nematodes

The dietary choices of bacterial-feeding nematodes could control the structure and ecological functions of soil bacterial communities. However, the physiological basis for the selection of particular bacterial species as food, and the consequences of these dietary choices for the survival of bacterial-feeding nematodes, is poorly understood. The objectives of this study were (1) to determine how nematode feeding preference was related to bacterial traits (cell size, gram stain and growth rate) and quality (water content, carbohydrate content, protein content and metabolite concentration), and (2) to evaluate how dietary choices affected the reproduction and lifespan of two soil-dwelling bacterial-feeding nematodes of the species Mesorhabditis and Acrobeloides. Their food sources included one model bacterium, Escherichia coli OP50, and four soil-dwelling bacterial species: Bacillus amyloliquefaciens, Bacillus megaterium, Variovorax paradoxus and Pseudomonas fluorescens. Both nematode species exhibited a similar hierarchy of diet choice, with P. fluorescens and E. coli OP50 being the most preferred food, whereas B. megaterium was the least preferred bacteria. Nematode feeding preference was strongly related to the water content, growth rate and metabolite concentration of bacterial cells, which explained 63–75% of the variation in the feeding preference index (PI, which indicates the number of nematodes attracted to specific bacteria), and the rest of the variation was attributed to bacterial cell size, gram stain, carbohydrate content and protein content. We propose two physiological mechanisms to explain dietary choices of bacterial-feeding nematodes: 1) chemical attraction to higher carbon dioxide levels around rapidly-growing bacteria or repulsion to volatile organic molecules released from bacterial cells, and 2) selective ingestion of bacterial cells with preferred characteristics (e.g., high water content in cells). Nematodes feeding on preferred bacteria always had higher reproduction, but dietary choices were not a good predictor of their lifespan. For example, Acrobeloides feeding on their preferred food P. fluorescens had the largest brood size but a moderate survival time. However, when Acrobeloides consumed their least-preferred food B. megaterium, they produced the smallest brood size and had the shortest survival time. This may be due to the fact that dietary resources are allocated first towards reproduction, and second to prolong the lifespan of bacterial-feeding nematodes. Our findings suggest that dietary choices are important for the survival of bacterial-feeding nematodes, and their ability to find and selectively ingest preferred bacterial species may have implications for soil bacterial community structure and ecological functions.