Latitudinal gradients in sea ice and primary production determine Arctic seabird colony size in Greenland

Sea ice loss will indirectly alter energy transfer through the pelagic food web and ultimately impact apex predators. We quantified spring-time trends in sea ice recession around each of 46 thick-billed murre (Uria lomvia) colonies in west Greenland across 20 degrees of latitude and investigated the magnitude and timing of the associated spring-time primary production. A geographical information system was used to extract satellite-based observations of sea ice concentration from the Nimbus-7 scanning multichannel microwave radiometer (SMMR, 1979-1987) and the Defence Meteorological Satellite Programs Special Sensor Microwave/Imager (SSMI, 1987-2004), and satellite-based observations of chlorophyll a from the moderate resolution imaging spectroradiometer (MODIS: EOS-Terra satellite) in weekly intervals in circular buffers around each colony site (150 km in radius). Rapid recession of high Arctic seasonal ice cover created a temporally predictable primary production bloom and associated trophic cascade in water gradually exposed to solar radiation. This pattern was largely absent from lower latitudes where little to no sea ice resulted in a temporally variable primary production bloom driven by nutrient cycling and upwelling uncoupled to ice. The relationship between the rate and variability of sea ice recession and colony size of thick-billed murres shows that periodical confinement of the trophic cascade at high latitudes determines the carrying capacity for Arctic seabirds during the breeding period.     

Latitudinal gradients in diversity: real patterns and random models

Mid-domain models have been argued lo provide a default explanation for the best known spatial pattern in biodiversity, namely the latitudinal gradient in species richness. These models assume no environmental gradients, but merely a random latitudinal association between the size and placement of the geographic ranges of species. A mid-domain peak in richness is generated because when the latitudinal extents of species in a given taxonomic group are bounded to north and south, perhaps by a physical constraint such as a continental edge or perhaps by a climatic constraint such as a critical temperature or precipitation threshold, then the number of ways in which ranges can be distributed changes systematically between the bounds. In addition, such models make predictions about latitudinal variation in the latitudinal extents of the distributions of species, and in beta diversity (the spatial turnover in species identities). Here we test how well five mid-domain models predict observed latitudinal patterns of species richness, latitudinal extent and beta diversity in two groups of birds, parrots and woodpeckers, across the New World. Whilst both groups exhibit clear gradients in richness and beta diversity and the general trend in species richness is acceptably predicted (but not accurately, unless substantial empirical information is assumed), the fit of these models is uniformly poor for beta diversity and latitudinal range extent. This suggests either that, at least for these data, as presently formulated mid-domain models are too simplistic, or that in practice the mid-domain effect is not significant in determining geographical variation in diversity.     

Latitudinal gradients in the species richness of Australian termites (Isoptera)

Abstract Using data on the geographic range of 260 described species in the Atlas of Australian Termites, seven ‘regions’ with more complete data, across a wide range of latitudes were selected for further analysis. For these regions, mean species richness (± SE) was calculated for (i) all species from all families, (ii) Termitidae (197 spp.), (iii) Amitermes spp. (Termitidae, 58 spp.), (iv) all families excluding Amitermes spp. (139 spp.), (v) Termopsidae (5 spp.), (vi) Kalotermitidae (32 spp.) and (vii) Rhinotermitidae (25 spp.). In addition, we compared the Atlas data with species richness for five regions, across a comparable range of latitudes, based on the pooled species richness of described and un-described species given in community studies. No group of termites showed a consistent decline in species richness from tropical to temperate latitudes for either data set. The Atlas data showed similar total species richness from the tropics to the mediterranean southwest, before declining to lowest species richness at the highest latitudes. Species richness of Amitermes spp. and Rhinotermitidae was highest in the southwest. Termopsidae and Kalotermitidae showed no latitudinal pattern in species richness. Community studies showed highest and lowest total species richness in the southwest and at the highest latitudes (south-coastal Western Australia), respectively, and similar species richness from the tropics to arid central Australia. Species richness of. Amitermes spp. was highest in the southwest (31 spp.). Kalotermitidae and Rhinotermitidae showed no clear latitudinal pattern. The latitudinal patterns of species richness for the Australian termites is consistent with that for the Australian vertebrates and ants in that they differ from patterns established for these taxa on other continents.     

Salt marsh vegetation: Latitudinal gradients in the zonation patterns

Summary Zonation patterns of salt marsh vegetation were examined at latitudes ranging from 44°40N at Halifax, Nova Scotia, to 58°50N at Churchill, Manitoba. It was found that in all areas examined the landward boundaries of the species' zones were more nearly coincident (i.e., more clustered) than their seaward boundaries. A conspicuous latitudinal trend was found: the clustering of both landward and seaward boundaries increased with increasing latitude. Evidence that between-species competition influences the locations of zone boundaries was also obtained. Possible implications of the results in terms of a relationship between intrapopulation polymorphism and latitude are discussed.     

Latitudinal patterns in the size of European butterflies

The importance of seasonality in shaping latitudinal size patterns was investigated in 16 species of lycaenine and satyrine butterflies with distributions in Sweden and continental Europe. Species without shifts in voltinism within the study area generally displayed clear size clines, increasing in size from north to south within Sweden. These species were also larger in continental Europe than in Sweden. In northern temperate areas a linear model for mean size at different latitudes seems to be a reasonable approximation for most species in this category. The size patterns for three species with shifts from univoltinism to bivoltinism at latitudes within Sweden were more reminiscent of the "saw-tooth"-pattern predicted by theory for such cases. The results suggest that size patterns in European butterflies to a large extent is governed by the length of the favorable season at different latitudes, affecting selection for development time and size. Altitude and drought also affect the effective season length and may amplify or complicate latitudinal patterns.     

Latitudinal gradients in Atlantic reef fish communities: trophic structure and spatial use patterns

Trophic strategies and spatial use habits were investigated in reef fish communities. The results supported the hypothesis of differential use of food resources among tropical and higher latitude reef fishes, i.e . the number of species and relative abundance of fishes relying on relatively low‐quality food significantly decreased from tropical to temperate latitudes. The species : genus ratio of low‐quality food consumers increased toward the tropics, and was higher than the overall ratio considering all fishes in the assemblages. This supports the view that higher speciation rates occurred among this guild of fishes in warm waters. It was also demonstrated that density of herbivorous fishes (the dominant group relying on low‐quality food resources) in the western Atlantic decreased from tropical to temperate latitudes. Spatial use and mobility varied with latitude and consequently reef type and complexity. Fishes with small‐size home ranges predominated on tropical coral reefs.     

Altruism and relatedness at colony foundation in social insects

Cooperative nest initiation in social insects is most easily explained when cooperating females are relatives, as is common in polistine wasps. However, recent research has revealed that unrelated ant queens also initiate colonies together. Reproductive dominance hierarchies are absent among unrelated foundresses, which contrasts with the rigid dominance hierarchies found among related foundresses. New field studies of joint nest founding among non-relatives show that cooperation is favored where colonies are clumped and brood raiding is common, so that attaining a large worker force quickly is critical to colony survival. These studies enrich our understanding of the role of relatedness in social groups.     

Queen size mediates queen survival and colony fitness in harvester ants

Abstract We examined the effect of queen size on the probability of new colony establishment in the ant Pogonomyrmex occidentalis. Large queens are significantly more likely to survive than small queens through the initial stages of colony founding. These differences in individual fitness correlates have corresponding effects on colony fitness. In species in which individual queens vary in fitness, sexual allocation ratios should incorporate the individual fitness functions.     

Latitudinal patterns in European ant assemblages: variation in species richness and body size

Using published distributions of 65 species from the British Isles and northern Europe, we show that ant assemblages change with latitude in two ways. First, as commonly found for many types of organisms, the number of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased significantly with region area. Second, although rarely demonstrated for ectotherms, the body size of ant species, as measured by worker length, increased significantly with increasing latitude. We found that this body-size pattern existed in the subfamily Formicinae and, to a lesser extent, in the Myrmicinae, which together comprised 95% of the ant species in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the pattern of increasing body size was due primarily to the ranges of ant species shifting to higher latitudes as their body sizes increased, with larger formicines becoming less represented at southerly latitudes and larger myrmicines becoming more represented at northerly latitudes. We conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hypotheses concerning phylogenetic history, the migration-ability hypothesis, and the starvation-resistance hypothesis.     

Colony size,social complexity and reproductive conflict in social insects

The broad limits of mature colony size in social insect species are likely to be set by ecological factors. However, any change in colony size has a number of important social consequences. The most fundamental is a change in the expected reproductive potential of workers. If colony size rises, workers experience a fall in their chances of becoming replacement reproductives and, it is shown, increasing selection for mutual inhibition of one another's reproduction (worker policing). As workers’ reproductive potential falls, the degree of dimorphism between reproductive and worker castes (morphological skew) can rise. This helps explain why small societies have low morphological skew and tend to be simple in organization, whereas large societies have high morphological skew and tend to be complex. The social consequences of change in colony size may also alter colony size itself in a process of positive feedback. For these reasons, small societies should be characterized by intense, direct conflict over reproduction and caste determination. By contrast, conflict in large societies should predominantly be over brood composition, and members of these societies should be relatively compliant to manipulation of their caste. Colony size therefore deserves fuller recognition as a key determinant, along with kin structure, of social complexity, the reproductive potential of helpers, the degree of caste differentiation, and the nature of within-group conflict.     

Genetic regulation of colony social organization in fire ants: an integrative overview

Expression of colony social organization in fire ants appears to be under the control of a single Mendelian factor of large effect. Variation in colony queen number in Solenopsis invicta and its relatives is associated with allelic variation at the gene Gp-9, but not with variation at other unlinked genes; workers regulate queen identity and number on the basis of Gp-9 genotypic compatibility. Nongenetic factors, such as prior social experience, queen reproductive status, and local environment, have negligible effects on queen numbers which illustrates the nearly complete penetrance of Gp-9. As predicted, queen number can be manipulated experimentally by altering worker Gp-9 genotype frequencies. The Gp-9 allele lineage associated with polygyny in South American fire ants has been retained across multiple speciation events, which may signal the action of balancing selection to maintain social polymorphism in these species. Moreover, positive selection is implicated in driving the molecular evolution of Gp-9 in association with the origin of polygyny. The identity of the product of Gp-9 as an odorant-binding protein suggests plausible scenarios for its direct involvement in the regulation of queen number via a role in chemical communication. While these and other lines of evidence show that Gp-9 represents a legitimate candidate gene of major effect, studies aimed at determining (i) the biochemical pathways in which GP-9 functions; (ii) the phenotypic effects of molecular variation at Gp-9 and other pathway genes; and (iii) the potential involvement of genes in linkage disequilibrium with Gp-9 are needed to elucidate the genetic architecture underlying social organization in fire ants. Information that reveals the links between molecular variation, individual phenotype, and colony-level behaviors, combined with behavioral models that incorporate details of the chemical communication involved in regulating queen number, will yield a novel integrated view of the evolutionary changes underlying a key social adaptation.     

Latitudinal patterns of egg size and maternal investment trade-offs in reef corals

Aim

The aims were to test the role of temperature in latitudinal patterns of egg size and investigate maternal investment trade-offs among coral taxa.

Location

Global, from 34° S to 34° N.

Time period

1981–2020.

Major taxa studied

Reef coral species from the order Scleractinia.

Methods

We compiled a comprehensive geo-referenced global dataset of egg sizes (diameter or volume) and fecundity (number of eggs per area) for colonial corals (Scleractinia; 123 species, 5359 observations and 39 localities), substantially enhanced by new field collections (>88% of observations). We used Bayesian phylogenetic multilevel models to test for Rass' rule (a hypothesized negative relationship between egg size and temperature); we also included other environmental variables and life history traits. We also tested whether a trade-off exists between egg size and fecundity in broadcast spawning hermaphroditic corals with horizontal symbiont transmission (HHT).

Results

We found a significant relationship between coral egg size and symbiont transmission. Eggs from coral species with vertical symbiont transmission were c. 18.8% smaller than those from species with horizontal symbiont transmission. We also found non-significant relationships between egg size and sea surface temperature (SST) for broadcast spawning corals and between egg size and fecundity specifically for HHT species.

Main conclusions

Contrary to recognized latitudinal patterns of egg size across taxa, our study does not provide support for Rass' rule in corals. Additionally, our findings do not support a maternal investment trade-off between egg size and fecundity for HHT species. Our study used a phylogenetic framework that should be a standard practice when studying interspecific variation, including investigation of maternal investment and identification of the influence of multiple predictors on larval fitness (egg size), in addition to trade-offs affecting propagule influx (fecundity). Both these functional traits are vital and have direct consequences for population maintenance and connectivity in sessile organisms, such as corals.     

The ecological benefits of larger colony size may promote polygyny in ants

How polygyny evolved in social insect societies is a long‐standing question. This phenomenon, which is functionally similar to communal breeding in vertebrates, occurs when several queens come together in the same nest to lay eggs that are raised by workers. As a consequence, polygyny drastically reduces genetic relatedness among nestmates. It has been suggested that the short‐term benefits procured by group living may outweigh the costs of sharing the same nesting site and thus contribute to organisms rearing unrelated individuals. However, tests of this hypothesis are still limited. To examine the evolutionary emergence of polygyny, we reviewed the literature to build a data set containing life‐history traits for 149 Palearctic ant species and combined this data set with a reconstructed phylogeny. We show that monogyny is the ancestral state and that polygyny has evolved secondarily and independently throughout the phylogenetic tree. The occurrence of polygyny is significantly correlated with larger colony size, dependent colony founding and ecological dominance. Although polydomy (when a colony simultaneously uses several connected nests) tends to occur more frequently in polygynous species, this trend is not significant when phylogenetic history is accounted for. Overall, our results indicate that polygyny may have evolved in ants in spite of the reduction in nestmate relatedness because large colony size provides immediate ecological advantages, such as the more efficient use of temporal food resources. We suggest that the competitive context of ant communities may have provided the conditions necessary for the evolution of polygyny in some clades.     

Importance of large colony size for successful invasion by Argentine ants (Hymenoptera: Formicidae): Evidence for biotic resistance by native ants

Abstract The Argentine ant, Linepithema humile (Mayr), is a widespread invasive ant species that has been associated with losses of native ant species and other invertebrates from its introduced range. To date, various abiotic conditions have been associated with limitations to the spread of Argentine ants, however, competitive interactions with native ant fauna may also affect the spread of Argentine ants. Here, we experimentally manipulated colony sizes of Argentine ants in the laboratory to assess whether Argentine ants were able to survive and compete for resources with a widespread, dominant native ant, Iridomyrmex‘rufoniger’. The results showed that over 24 h, the proportions of Argentine ants that were alive, at baits, and at sugar water decreased significantly in the presence of Iridomyrmex. In addition, Argentine ant mortality increased over time, however, the proportion of the colony that was dead decreased with the largest colony size. Argentine ants were only able to overcome Iridomyrmex when their colony sizes were 5–10 times greater than those of the native ants. We also conducted trials in which colonies of Argentine ants of varying sizes were introduced to artificial baits occupied by Iridomyrmex in the field. The results showed that larger Argentine ant colonies significantly affected the foraging success of Iridomyrmex after the initial introduction (5 min). However, over the first 20 min, when the Argentine ants were present at the baits, and over the entire 50 min experimental period, the numbers of Iridomyrmex at baits did not differ significantly with the size of the Argentine ant colony. This is the first experimental study to investigate the role of colony size in the invasion biology of Argentine ants in Australia, and the results suggest that Iridomyrmex may reduce the spread of Argentine ants, and that Argentine ants may need to attain large colony sizes in order to survive in the presence of Iridomyrmex. We address the implications of these findings for the invasion success of Argentine ants in Australia, and discuss the ability of Argentine ants to attain large colony sizes in introduced areas.     

The role of colony organization on pathogen transmission in social insects

Social organisms are especially vulnerable to pathogens due to the homogeneity of the colony, and the close proximity and extensive interactions among its members. However, the social organization of these groups also offers the potential to provide an effective barrier against the transmission of pathogens within the colony. Social insects with their elaborate colony organizations provide an ideal model system to develop and test this hypothesis. While the different elements of colony organization are generally assumed to be products of ergonomic selection, in this paper we address how the same elements could influence the transmission of pathogens. By developing a simple model, we explore how three parameters of colony organization, division of labor, interaction network and colony demography could influence the transmission of pathogens. We find that heterogeneity among individuals in terms of division of labor alone has little effect on the spread of an infection in the colony and the scenario is indistinguishable from one in which all the individuals are homogeneous. However, division of labor, combined with heterogeneity in the interaction network and demographic schedules reduce the spread of an infection.     

Latitudinal and depth gradients in marine predation pressure

Aim There is a general paradigm that marine predation pressure increases towards the tropics and decreases with depth. However, data demonstrating global trends are generally lacking. Rhynchonelliform brachiopods inhabit all the oceans and often survive shell‐crushing predator attacks. We investigate shell repair in brachiopods across a range of Southern Hemisphere and tropical Northern Hemisphere latitudes and depths. Location The Southern Hemisphere and tropical Northern Hemisphere. Methods We analysed the frequency of shell repair in 112 bulk samples, over 70% of which showed traces of shell damage and repair. Results The pattern of shell repair frequency (RF) was more complicated than the anticipated increase with decreasing latitude, with low levels at both polar and tropical sites but high levels at temperate latitudes. This pattern is only evident, however, in shallow water assemblages; and there is no latitudinal trend in water depths greater than 200 m, where shell RF is systematically low. There was a significant logarithmic relationship between RF and depth. Low polar repair rates reflect reduced predation pressure, directly supporting the global paradigm. Low rates in the tropics appears counter to the paradigm. However, tropical brachiopods are generally very small (micromorphic) in shallow water and below the minimum size at which damage is recorded anywhere. Main conclusions Predation pressure decreased logarithmically with depth. At shallow depths (< 200 m) RF showed its highest levels in the mid temperate latitudes with decreasing frequency towards both the tropics and the poles. Low levels of shell repair at high latitudes are likely to be due to a lack of crushing predators, but in the tropics it is suggested that the low frequency is a result of the small size of tropical brachiopods. We hypothesize that micromorphy in this region may be an outcome of high predation pressure.