Differences In Reproductive Output Research Articles

Sexual conflict underlying external female genital mutilation in spiders: assessing whether females benefit from multiple matings.

External female genital mutilation (EFGM) is a type of traumatic mating in which males damage female genitalia, resulting in the loss of female re-mating ability. This study examined whether sexual conflict underlies EFGM by examining the possible female reproductive costs from the decreased number of matings in spider, Cyclosa argenteoalba. The female typically receives sperm from a male twice during a mating bout. We manipulated both the number of matings and the number of male partners of females and compared their reproductive outputs. The results indicated that females receiving sperm three times-equivalent to one and a half matings from two males-laid more egg sacs with more eggs per egg sac than control females that received sperm twice from one male. The control females laid more egg sacs and fewer eggs per egg sac than females that received sperm once. There was no significant difference in reproductive output between the control females and females that received sperm twice from the two males. These results indicate that females benefit from multiple matings but not from mating with multiple males, supporting the sexual conflict hypothesis. Our study has implications for our understanding of the evolution of harmful mating.

Temporal and spatial variation in reproductive benefits in a partial migrant.

In partial migrant systems, where residents and migrants coexist within a population, residents are commonly predicted to gain a reproductive advantage over migrants through priority access to high-quality territories and an earlier breeding start. Annual variation in reproductive benefits has been suggested to be important for the coexistence of both strategies in a population, as differences in wintering conditions experienced by the two strategies may result in a periodic reproductive advantage for migrants. However, the importance of spatial environmental variation for reproductive output in partially migrant populations remains largely unexplored. We investigated variation in the reproductive output of migrants and residents in a population of Swiss red kites (Milvus milvus) both temporally, across and within years, and spatially, along an elevational gradient. We gathered 4 years of reproductive data combined with 183 GPS-derived full annual cycles from individuals breeding in the Swiss Alpine foothills. At low, but not high, elevations, residents produced more fledglings than migrants. We also found evidence for annual variation in the reproductive advantage of the two strategies. Furthermore, while reproductive output did decline with a later breeding start, there was no difference in the start of breeding between the two migration strategies. The results of this study suggest that differences in reproductive output between migrants and residents in partial migrant populations can vary both due to the use of spatially distinct overwintering grounds and because the strategies are differently affected by spatial variables in the breeding area, such as elevation. The study emphasizes that spatial and temporal variation in reproductive benefits must be considered when predicting how migratory species will respond to future environmental change.

Feather growth rate and hormone deposition vary with elevation but not reproductive costs in resident Mountain Chickadees

Abstract Many organisms engage in metabolic tradeoffs to manage costs associated with reproductive output which often leads to these costs carrying over into the future. Compensatory mechanisms vary across life history strategies and are expected to result in near-optimal fitness gains for the investor. Here we investigated whether environmental differences associated with increasing montane elevation and variation in reproductive output of a resident passerine songbird, the Mountain Chickadee (Poecile gambeli), were related to physiological conditions during annual molt. Higher elevations are associated with harsher environmental conditions during the winter, which results in later and shorter breeding seasons than at lower elevations. We sampled the outermost tail feathers from adult birds in the fall after their prebasic molt, which initiates closely after reproduction (e.g., after parental care has ceased, ~1–3 weeks). We measured the hormone corticosterone deposited in feathers (fCORT) and feather growth rates for evidence of physiological effort predicted to be driven by several units of reproductive output (e.g., breeding timing, clutch and brood size, and offspring mass). There were no relationships between any measure of reproductive output and feather characteristics between elevations or across years, despite substantial variation in reproductive output in the wider population across this same time. However, birds at the high-elevation site grew their tail feathers significantly faster and had higher fCORT deposition compared to low-elevation birds. These results suggest that although differences in reproductive output and any related signals of associated physiological effort (e.g., fCORT and feather growth rate) may not extend into individual conditions during annual molt, shorter breeding seasons associated with harsher environmental conditions may favor faster feather growth as required by earlier onset of winter.

Demography across latitudinal and elevational gradients for range-expanding whelks

Marine species worldwide are responding to ocean warming by shifting their ranges to new latitudes and, for intertidal species, elevations. Demographic traits can vary across populations spanning latitudinal and elevational ranges, with impacts on population growth. Understanding how demography varies across gradients from range center to edge could help us predict future shifts, species assemblages, and extinction risks. We investigated demographic traits for 2 range-expanding whelk species: Acanthinucella spirata and Mexacanthina lugubris. We measured reproductive output across environmental (latitudinal and shore elevation) gradients along the coast of California, USA. We also conducted intensive measurements of offspring condition (survival and thermal tolerance) across shore elevation for M. lugubris at one site. We found no difference in reproductive output, body size, or larval survival across shore heights for M. lugubris, suggesting that egg-laying behavior buffers developing stages from the relatively high level of thermal variation experienced due to daily tidal emersion. However, across latitudes, reproductive output increased toward the leading range edge for A. spirata, and body size increased for both species. Increased vital rates at the leading range edge could increase whelk population growth and expansion, allowing species to persist under climate change even if contractions occur at trailing edges.

Flight-reproduction trade-offs are weak in a field cage experiment across multiple Drosophila species

Flight-reproduction trade-offs, such that more mobile individuals sacrifice reproductive output (e.g., fecundity) or incur fitness costs, are well-studied in a handful of wing-dimorphic model systems. However, these trade-offs have not been systematically assessed across reproduction-related traits and taxa in wing monomorphic species despite having broad implications for the ecology and evolution of pterygote insect species. Here we therefore determined the prevalence, magnitude and direction of flight-reproduction trade-offs on several fitness-related traits in a semi-field setting by comparing disperser and resident flies from repeated releases of five wild-caught, laboratory-reared Drosophila species, and explicitly controlling for a suite of potential confounding effects (maternal effects, recent thermal history) and potential morphological covariates (wing-loading, body mass). We found almost no systematic differences in reproductive output (egg production), reproductive fitness (offspring survival), or longevity between flying (disperser) and resident flies in our replicated releases, even if adjusting for potential morphological variation. After correction for false discovery rates, none of the five species showed evidence of a significant fitness trade-off associated with increased flight (sustained, simulated voluntary field dispersal). Our results therefore suggest that flight-reproduction trade-offs are not as common as might have been expected when assessed systematically across species and under the relatively standardized conditions and field setting employed here, at least not in the genus Drosophila. The magnitude and direction of potential dispersal- or flight-induced trade-offs, and the conditions that promote them, clearly require closer scrutiny. We argue that flight or dispersal is either genuinely cheaper than expected, or the costs manifest differently than those assessed here. Lost opportunities (i.e., time spent on mate-finding, mating or foraging) or nutrient-poor conditions could promote fitness costs to dispersal in our study system and that could be explored in future.

Variation in pollen sterility and gender specialization: an investigation with distylous species of Erythroxylum (Erythroxylaceae)

Differences in pollen sterility between morphs in distylous populations may represent the first step in the evolution of gender specialization. Theoretically, for partially or completely male sterile individuals to persist they must have some fitness advantage that compensates for the loss of male function. Gender specialization is considered a widespread process in Erythroxylum, but male sterility and the resource reallocation to female function have been investigated in few species and populations. In 18 populations of four distylous species of Erythroxylum, we quantified the levels of male sterility, estimated through pollen sterility, in short- and long-styled flowers to test if sterility is morph-biased. In one population per species, we also described the frequency of floral visitors, the production of flowers and fruits, and the quality of fruits and seeds of short- and long-styled plants to evaluate the expression of trade-offs in allocation to male and female function. In some populations of E. campestre and E. deciduum, short-styled flowers possessed higher levels of pollen sterility than long-styled flowers. Although most flowers of E. suberosum and E. tortuosum also expressed pollen sterility, the frequency of sterility was similar between morphs in all populations. Differences in reproductive output between morphs occurred only in populations of species with morph-biased sterility, but none of the variations reflect resource allocation to female fitness of short-styled plants. Differences in the level of sterility between morphs indicates the potential for gender specialization in populations of E. campestre and E. deciduum, despite the apparent lack of a trade-off in allocation.

Flowering phenology and reproduction of a forest understorey plant species in response to the local environment

Temperate forest understorey plants are subjected to a strong seasonality in their optimal growing conditions. In winter and early spring, low temperatures are suboptimal for plant growth while light becomes limited later in spring season. We can thus expect that differences in plant phenology in relation to spatiotemporal environmental variation will lead to differences in reproductive output, and hence selection. We specifically studied whether early flowering, a paradoxical pattern that is observed in many plant species, is an adaptive strategy, and whether selection for early flowering was confounded with selection for flower duration or was attributable to environmental variables. We used Geum urbanum as a study species to investigate the effect of relevant environmental factors on the species’ flowering phenology and the consequences for plant reproductive output. We monitored the phenology of four to six plants in each of ten locations in a temperate deciduous forest (Belgium). We first quantified variation in flowering time within individuals and related this temporal variation to individual flower reproductive output. Then, we studied inter-individual variation here-in and linked this to reproduction at the plant level, hence studying the selection differential. We found that flowering within individual plants of Geum urbanum was spread over a long period from June to October. Reproductive output of individual flowers, measured as total seed mass per flower, declined during the season. We found no indication for selection for early flowering but rather for longer flower duration. Larger plants had an earlier flowering onset and a higher seed mass, which suggests that these factors covary and are condition dependent. None of the studied environmental variables could explain plant size, although soil pH and to a lesser extent light availability had a positive direct effect on seed mass per plant. Finally, we suggest that the high intra-individual variation in flowering time, which might be a risk spreading strategy of the plant in the presence of seed predation, limits the potential for selection on flowering phenology.

Individual differences determine the strength of ecological interactions

Biotic interactions are central to both ecological and evolutionary dynamics. In the vast majority of empirical studies, the strength of intraspecific interactions is estimated by using simple measures of population size. Biologists have long known that these are crude metrics, with experiments and theory suggesting that interactions between individuals should depend on traits, such as body size. Despite this, it has been difficult to estimate the impact of traits on competitive ability from ecological field data, and this explains why the strength of biotic interactions has empirically been treated in a simplistic manner. Using long-term observational data from four different populations, we show that large Trinidadian guppies impose a significantly larger competitive pressure on conspecifics than individuals that are smaller; in other words, competition is asymmetric. When we incorporate this asymmetry into integral projection models, the predicted size structure is much closer to what we see in the field compared with models where competition is independent of body size. This difference in size structure translates into a twofold difference in reproductive output. This demonstrates how the nature of ecological interactions drives the size structure, which, in turn, will have important implications for both the ecological and evolutionary dynamics.

A systematic review of the direct and indirect effects of herbivory on plant reproduction mediated by pollination.

BackgroundPlant reproduction is influenced by the net outcome of plant–herbivore and plant–pollinator interactions. While both herbivore impacts and pollinator impacts on plant reproduction have been widely studied, few studies examine them in concert.MethodologyHere, we review the contemporary literature that examines the net outcomes of herbivory and pollination on plant reproduction and the impacts of herbivores on pollination through damage to shared host plants using systematic review tools. The direct or indirect effects of herbivores on floral tissue and reported mechanisms were compiled including the taxonomic breadth of herbivores, plants and pollinators.ResultsA total of 4,304 studies were examined producing 59 relevant studies for synthesis that reported both pollinator and herbivore measures. A total of 49% of studies examined the impact of direct damage to floral tissue through partial florivory while 36% of studies also examined the impact of vegetative damage on pollination through folivory, root herbivory, and stem damage. Only three studies examined the effects of both direct and indirect damage to pollination outcomes within the same study.ConclusionsIt is not unreasonable to assume that plants often sustain simultaneous forms of damage to different tissues and that the net effects can be assessed through differences in reproductive output. Further research that controls for other relative drivers of reproductive output but examines more than one pathway of damage simultaneously will inform our understanding of the mechanistic relevance of herbivore impacts on pollination and also highlight interactions between herbivores and pollinators through plants. It is clear that herbivory can impact plant fitness through pollination; however, the relative importance of direct and indirect damage to floral tissue on plant reproduction is still largely unknown.

Positive effects of set-asides on European hare (Lepus europaeus) populations: Leverets benefit from an enhanced survival rate

Abstract Since agricultural intensification started in the early 1900s, farmland biodiversity in Europe has decreased. Non-farmed features are of high importance for the promotion of plant and animal species including the European hare (Lepus europaeus). As an immediate cause of the decline in European hare abundances, a reduction in reproductive success has been proposed. Female fertility is not impaired and leveret mortality is inherently high in this lagomorph species. However, hunting bags suggest that leveret mortality has increased in recent decades. We studied the effect of set-asides on population trends of hunted European hares by analysing data of spotlight counts and of hunting bags in arable landscapes in Lower Austria during six years. We found no interannual and interareal differences in reproductive output of adult females. Accordingly, female reproductive output had no effect on population growth of the hares. Leveret survival rate was higher in the study sites with a high proportion of set-asides (9 and 13%) than in the sites with a lower proportion of set-asides (3 and 5%). We recorded a positive effect of leveret survival rate on population growth and next year's spring density. Moreover, the proportion of set-asides positively affected spring density, population growth, hunting bag, leveret survival rate and number of subadults in autumn. Hence, set-asides contribute to the survival of leverets and, correspondingly, population growth and spring density. Accordingly, set-asides are a highly important habitat measure and an evidence-based conservation tool for the promotion of this species in arable landscapes.

Do agricultural environments increase the reproductive success of White Stork Ciconia ciconia populations in South-Western Poland?

As populations of White Stork Ciconia ciconia have decreased at different rates in Europe, the specific environmental drivers that influence breeding success are a matter of controversy. Here we use body size, blood, and environmental data of a total of 1226 stork nestlings of different ages from a total of 363 nests in three different habitats (meadows, forest-edges, open agricultural landscapes) in S-W Poland to ask whether: 1) natural grassland environments increase the reproductive output in comparison with agricultural landscapes, 2) nestlings from agricultural landscapes differ in health status from nestlings in more natural habitats, 3) differences in environmental stress translate into respective differences in reproductive output and health status of nestlings. There was no significant difference in age corrected body mass and in the temporal increase in nestling mass between the study sites. Clutch sizes were highest and age corrected total clutch mass lowest at the meadow sites while agricultural and woodland sites did not significantly differ. Hemoglobin and red blood cell content were lowest and white blood cell and blood antioxidant concentrations were highest in the meadows indicating higher degrees of environmental stressors. These blood parameters varied strongly among study years. Our study does not confirm that agricultural landscapes are less suited for stork breeding success. We even find some indication of a better health status of nestlings in agricultural environments that might compensate smaller clutch sizes. Our data indicate that reproductive output is multifaceted. As we found some indication of a trade-off between clutch size and health status we argue that only multiple metrics of reproductive success are able to assess the long-term effect of habitat choice on fitness.

Good times, bad times: inter-annual reproductive output in a montane endemic succulent (Aloe peglerae; Asphodelaceae) driven by contrasting visitor responses of small mammals and birds

The movements of birds and small mammals may be affected by spatial and temporal variation in resource availability. For the genus Aloe, bird abundance and diversity increase in response to increases in nectar availability during flowering. Aloe peglerae Schönland, endemic to the Magaliesberg Mountain Range, South Africa, is primarily pollinated by the Cape rock-thrush (Monticola rupestris), but the nocturnal Namaqua rock mouse (Micaelamys namaquensis) contributes to pollination. To test the independent contributions of different pollinator guilds, i.e. birds and small mammals, we conducted selective pollinator exclusion experiments during two consecutive flowering seasons – one ‘good’ year and one ‘poor’ year (14 and 7% of plants flowering respectively). Reproductive output for both years was measured for A. peglerae plants assigned to selective exclusion treatments: (i) no visitors; (ii) nocturnal visitors; (iii) diurnal visitors; and (iv) all visitors, with camera traps recording visitors to each treatment. Bird visitation rates to the ‘diurnal visitors’ treatment were higher during the good year; subsequently, reproductive output in the poor year was lower, with plants in this treatment producing no fruit in the poor flowering year. In the ‘nocturnal visitors’ treatment, nocturnal visitation rates were similar with no significant difference in reproductive output between years. Seed viability was maintained between years, although less seed was produced during the poor flowering season. Mobile birds are less abundant in the A. peglerae population during poor flowering years – years when nectar resources are less abundant than in good flowering years, resulting in reduced plant reproductive output. However, the presence of non-flying, small mammals that cannot relocate to better feeding grounds compensates for the absence of birds in poor flowering years. This aloe may be resilient against Allee effects in the absence of primary pollinators. Nonetheless, conservation of A. peglerae should still be prioritised since low flowering densities and ongoing anthropogenic disturbance could be detrimental to the species’ survival.

Comparative reproductive output of two cellar spiders (Pholcidae) that coexist in southwest Ohio

Species differ in their reproductive abilities, which may affect their success. In southwest Ohio, populations of Pholcus phalangioides (Fuesslin, 1775) (Araneae: Pholcidae) have largely been replaced by Pholcus manueli Gertsch, 1937 (Araneae: Pholcidae). We suspected that differences in reproductive output underpinned the success of P. manueli. We documented the reproductive success of both species in the laboratory. Female P. phalangioides mated more readily and were more likely to produce eggsacs than P. manueli, but the timing of eggsac production and spiderling emergence were similar. The eggsacs of P. phalangioides contained smaller numbers of larger eggs but similar numbers of spiderlings emerged from the sacs of both species. We uncovered a negative relationship between egg size and number for P. phalangioides, but not for P. manueli. Our results do not explain the relative success of P. manueli, however, we have uncovered differences in the reproductive strategies utilized by these ecologically-similar congeners.

Effect of maternal foraging habitat on offspring quality in the loggerhead sea turtle (Caretta caretta).

Exploring a trade‐off between quantity and quality of offspring allows differences in the fitness between alternative life histories to be accurately evaluated. We addressed the mechanism that maintains alternative life histories (small oceanic planktivores vs. large neritic benthivores) observed in a loggerhead sea turtle (Caretta caretta) population, which has been suggested to be environmental, based on the lack of genetic structure and a large difference in reproductive output. We examined whether maternal foraging habitat affects offspring quality, by measuring the morphology, emergence success, and righting response of hatchlings following incubation in a common open sand area over the whole nesting season at Yakushima Island, Japan, and by recording early growth and survival of offspring that were reared in a common environment at a Japanese aquarium. Furthermore, we tested whether sea turtles adjust egg size in response to temporal shifts of the incubation environment. There were no significant differences in any hatchling traits between oceanic and neritic foragers (which were classified by stable isotope ratios), except for clutches laid during the warmest period of the nesting season. There were also no significant differences in the growth and survival of offspring originating from the two foragers. The size of eggs from both foragers significantly increased as the season progressed, even though the rookery had heavy rainfall, negating the need to counteract heat‐related reduction in hatchling morphology. In comparison, the sizes of adult body and clutches from both foragers did not vary significantly. The results further support our previous suggestions that the size‐related foraging dichotomy exhibited by adult sea turtles does not have a genetic basis, but derives from phenotypic plasticity. Adjustment in reproductive investment may be associated with: (1) predation avoidance, (2) founder effect, and/or (3) annual variation in egg size.

Selecting plant species and traits for phytometer experiments. The case of peatland restoration

Abstract Phytometers are indicator transplants that provide information on site conditions based on plant survival, growth and reproduction. Since this is a relatively new approach, standards for its implementation remain to be defined, for example, during peatland restoration. Peatland restoration frequently aims at recovering characteristic communities, and a key attribute of successfully restored ecosystems is their capacity to sustain viable populations of target species. When not actively introduced, these species are expected to establish on their own after improving site conditions, for example by rewetting. Assessments to determine whether this goal is met require the long-term monitoring of species’ presence, whereas the underlying causes of these observations, i.e. site or dispersal limitation, often remain unknown. Using phytometers within ecological restoration helps addressing this question. The goal of this study is to compare the responses of several species and traits to environmental conditions in restored peatlands. Three target species (Drosera rotundifolia, Eriophorum vaginatum, Vaccinium oxycoccos) were planted in restored montane peatlands in central Germany, while in a greenhouse experiment, the same species were grown on peat from the field sites and exposed to two water levels. Several plant traits were measured and compared with variation in light, water and soil conditions. The response to habitat conditions was species-specific, indicating that the use of different phytometers increases the reliability of monitoring. Survival and growth traits were suitable to assess a wide range of abiotic conditions, while differences in reproductive output were more time-consuming to measure. Survival provided the most conclusive results for species sensitive to stressful habitat conditions. Biomass and other size metrics of the phytometers, as well as growth and reproductive traits were partly redundant. Thus, we suggest recording survival and biomass and use non-destructive growth measurements for repeated assessments, while the choice of the most suitable size trait should depend on the growth form. Our study stresses the potential of phytometers for monitoring the restoration outcome, while highlighting the importance of species and trait selection.

Female mate preference in an invasive phytopathogen vector: how learning may influence mate choice and fecundity in Diaphorina citri

AbstractIn some arthropods, females learn in the context of reproduction to refine their mate choices and avoid males displaying traits associated with impotency. Previous studies have shown that males of the Asian citrus psyllid, Diaphorina citriKuwayama (Hemiptera: Psyllidae), associate female odor with copulatory rewards. However, it is unclear whether females similarly learn about male traits. We compared mate choice in females previously mated to either blue or orange males and found that females may associate male color with reproductive success, and avoided blue males after previous experience. Orange males mated more frequently than blue males and appeared to be more sexually aggressive in their mating attempts. In addition, females mated to orange males laid approximately twice as many eggs as those mated to blue males. We dissected male psyllids and measured the size of their reproductive organs to determine whether abdominal color was associated with reproductive development. Our morphometric analysis indicated that blue males may not be physiologically immature compared with orange males. Rather, blue males displayed larger testes and seminal vesicles than orange males, suggesting that differences in reproductive output may be behavioral in nature. Based on our data, we suggest that females learn about the appearance and mating behaviors of blue and orange males from early mating experiences, and subsequently avoid blue males in future matings. Although the roles of blue males within a population are unclear, it is possible that blue morphs may specialize in other functions such as dispersal.

A New Report of Nezara viridula f. aurantiaca (Heteroptera: Pentatomidae) from a Cultured Population in Washington County, Mississippi.

Nezara viridula adult coloration can vary, including a rare orange-colored type (i.e., N. viridula f. aurantiaca). In November 2015, three Nezara viridula males displaying orange coloration were found in an established colony in Stoneville, MS. The objectives of this study were to determine if alleles of these orange types conformed to the allele characteristics previously reported for N. viridula f. aurantiaca and to determine if there were any differences in reproductive output compared with the green-colored type. The three orange-type males were crossed with green-type females to produce a hybrid F1. The F1 progeny was allowed us to cross to produce an F2. The F2 progeny consisted of 672 green females, 351 green males, 298 orange males, and 0 orange females. These ratios did not differ significantly from the expected 50:25:25:0 ratios for a single recessive sex linked allele for color phenotype. The F2 cross of green females and orange males produced an F3 consisting of 345 green females, 346 green males, 100 orange females, and 85 orange males. These ratios also conformed to the expected ratios (0.375:0.375:0.125:0.125) with the exception of orange males, which numbers were slightly lower than expected. The pure orange type N. viridula produced significantly less egg masses (0.71 ± 0.15) per day than green types (2.09 ± 0.16) and their reproductive output, measured as net reproductive rate (Ro), was lower in orange (13.71) compared with green (20.67) types.

The reproductive ecology ofMononeuria patula(Michx.) Dillenb. and Kadereit (Caryophyllaceae)1

Mononeuria patula (Michx.) Dillenb. and Kadereit (formally known as Minuartia patula; Caryophyllaceae) is a winter annual found in barrens, glades, rocky outcrops, and dolomite prairies of the eastern and central United States. This species is rare in Illinois, Indiana, and Ohio, and vulnerable in Kentucky, Missouri, and Virginia. In a two-year study we examined several aspects of the reproductive ecology of M. patula at five populations in northeastern Illinois. We used a combination of field-based studies (i.e., fruit set and seed set, breeding system, population size estimation), field observations (i.e., phenology), laboratory studies (i.e., seed germination, pollen:ovule ratio, floral morphometrics) and historical data (i.e., population size and weather data) to answer several questions: (1) What can data on the reproductive ecology of M. patula tell us about the species?; (2) Are there differences in reproductive output among populations of M. patula?; and (3) Can variation in the population size of M. patula be related to reproductive output and/or local weather patterns? Based on caging studies, flower phenology, and pollen to ovule ratio, M. patula can be considered a facultative autogamous species. Also, although significant differences were found among populations of M. patula for fruit set, seed set, and seed germination, fruit set was relatively high (above 60%), but seed set and seed germination were relatively low (less than 50%) regardless of the population. No correlation was found between population size and reproductive output or local weather data. The results of this study can be used to develop a conservation strategy for M. patula across its range in the U.S.

Nascent multicellular life and the emergence of individuality.

The evolution of multicellular organisms from unicellular ancestors involves a shift in the level at which selection operates. It is usual to think about this shift in terms of the emergence of traits that cause heritable differences in reproductive output at the level of nascent collectives. Defining these traits and the causes of their origin lies at the heart of understanding the evolution of multicellular life. In working toward a mechanistic, take-nothing-for-granted account, we begin by recognizing that the standard Lewontin formulation of properties necessary and sufficient for evolution by natural selection does not necessarily encompass Darwinian evolution in primitive collectives where parent-offspring relationships may have been poorly defined. This, we suggest, limits the ability to conceptualize and capture the earliest manifestations of Darwinian properties. By way of solution we propose a relaxed interpretation of Lewontin's conditions and present these in the form of a set of necessary requirements for evolution by natural selection based upon the establishment of genealogical connections between recurrences of collectives. With emphasis on genealogy - as opposed to reproduction - it is possible to conceive selection acting on collectives prior to any manifestation of heritable variance in fitness. Such possibility draws attention to the evolutionary emergence of traits that strengthen causal relationships between recurrences - traits likely to underpin the emergence of forms of multiplication that establish parent-offspring relationships. Application of this framework to collectives of marginal status, particularly those whose recurrence is not defined by genealogy, makes clear that change at the level of collectives need not arise from selection acting at the higher level. We conclude by outlining applicability of our framework to loosely defined collectives of cells, such as those comprising the slugs of social amoeba and microbes that constitute the human microbiome.

Both like it hot? Influence of temperature on two co-occurring intertidal barnacles in central Chile

Jehlius cirratus and Notochthamalus scabrosus, two chthamalid barnacles common to the upper rocky intertidal coast of Chile, often overlap extensively in their vertical distribution, with Jehlius extending slightly higher on the shore. Previous studies examining competition between Jehlius and Notochthamalus have come to differing conclusions regarding the nature and direction of their relationship within a hierarchy for space, but together suggest that temperature may play an important part in meditating their competitive interactions. Here, we address the role of temperature during emersion on Jehlius and Notochthamalus via species-specific responses in abundance, growth and reproduction to varying thermal conditions during tidal emersion. Results from a shading experiment conducted at two high intertidal elevations indicated that both species responded similarly to reduced temperatures in terms of abundance and space occupation. Growth rates differed between species, however, suggesting that Notochthamalus may be more limited by higher temperature than Jehlius, but growth rates of both species were similar under the warmest (high zone, unshaded) and coolest (mid zone, shaded) treatments. Although we found a greater proportion of Notochthamalus individuals brooding eggs in unshaded control areas (where sample size allowed analysis) and greater numbers of Jehlius individuals brooding under shades, no differences in reproductive output (egg mass) were found among brooding individuals between shading treatments and tidal elevation for either species. Overall, we found no evidence of temperature mediated tradeoffs in performance between adult Jehlius and Notochthamalus. Instead, our results indicate a lack of a strong competitive hierarchy between Jehlius and Notochthamalus and suggest that temperatures experienced during emersion may reinforce vertical patterns of adult abundance established during settlement.