Mutualism or Parasitism? Using a Phylogenetic Approach to Characterize the Oxpecker-Ungulate Relationship

With their striking predilection for perching on African ungulates and eating their ticks, yellow-billed (Buphagus africanus) and red-billed oxpeckers (B. erythrorhynchus) represent one of the few potentially mutualistic relationships among vertebrates. The nature of the oxpecker–ungulate relationship remains uncertain, however, because oxpeckers are known to consume ungulate tissues, suggesting that the relationship between oxpeckers and ungulates may also be parasitic. To examine this issue further, we obtained data on oxpecker preferences for different ungulate species, the abundance of ticks on these ungulates, and ungulate hide thickness. In support of the mutualism hypothesis, we found that both species of oxpeckers prefer ungulate hosts that harbor a higher abundance of ticks. We found no evidence that hide thickness—a measure of the potential for parasitism by oxpeckers—predicts oxpecker preferences for different ungulate species. Oxpeckers also prefer larger-bodied ungulates, possibly because larger animals have more ticks, provide a more stable platform upon which to forage, or support more oxpeckers feeding simultaneously. However, the preference for ungulates with greater tick abundance was independent of host body mass. These results support the hypothesis that the relationship between oxpeckers and ungulates is primarily mutualistic.Human Evolutionary Biolog

Spatial Synchrony of Monarch Butterflies

I examined spatial synchrony in Populations of monarch butterflies (Danaus plexippus) during the summer breeding season across North America and while overwintering along the Pacific Coast. Spatial synchrony was observed in all analyses, but was particularly great among eastern summer populations and among overwintering populations on the Pacific Coast. Thus, in a year when relatively large numbers of monarchs were found at a particular breeding or wintering site in these populations, other sites within a wide area were likely to have relatively large numbers of monarchs as well. Spatial structure, measured by the decline in synchrony with distance, was relatively strong among summer populations in eastern North America, weaker, but present, among western Summering populations and virtually nonexistent among overwintering populations along the Pacific Coast. Spatial synchrony in mean temperatures during the relevant time periods was generally much greater than that observed in the monarchs, consistent with the hypothesis that environmental factors (the Moran effect) may be playing a central role in causing the observed population sync,irony. However, differences in spatial structure between monarch populations and mean temperature during the summer suggest that other factors, possibly post-migratory dispersal, are also affecting synchrony. Dispersal is particularly likely to be important in determining the amusual lack of spatial Structure observed in overwintering populations of monarchs, which are believed to mix over wide areas during fall migration

Abbreviated inner primaries: a sex-linked dimorphism in the acorn woodpecker

In at least 15 species of woodpeckers, the inner primaries of nestlings are reduced in size. This trait is polymorphic in Acorn Woodpeckers (Melanerpes formicivorus) at Hastings Reservation in central coastal California, where most nestlings (90.1%) had reduced first and second primaries, 9.8% had only a reduced first primary, and 0.1% had no reduced primaries. More males (11.1%) had large second primaries than did females (5.3%), and females with this trait were less likely to survive their first year of life. Smaller inner primaries may provide a temporary energetic savings for nestlings that facilitate faster growth, but, if so, why this trait is not more common among other cavity-nesting species remains unknown. This trait appears to be more ecologically interesting than previously suspected and warrants study in other species and populations of woodpeckers

Seychelles warblers: complexities of the helping paradox

IntroductionThe Seychelles warbler (Acrocephalus sechellensis), a passerine endemic to the Seychelles archipelago, is a facultatively cooperative breeder that lives either in pairs or small groups. Breeding groups normally consist of a dominant pair and one to three subordinates, although up to nine have been observed. Subordinates can be of either sex, and are often offspring that have delayed dispersal and remained in their natal territory (Komdeur 1992; Richardson et al. 2002; Eikenaar et al. 2008, 2010). By the 1960s the last remnant population of this then critically endangered species was confined to Cousin Island (Figure 12.1). Subsequent conservation actions, including the restoration of forest habitat and the establishment of new populations through translocations, have provided unique opportunities to study the evolutionary ecology of cooperative breeding in this species. We have followed the entire world population of the Seychelles warbler since our study started in 1981. In 1997, however, we increased the intensity of work on Cousin and since then nearly all individuals, including fledglings, have been captured, ringed, blood sampled, sexed, and monitored for breeding and status. Molecular tools have been used to assign the sex and genetic parentage of young birds and to determine levels of relatedness between individuals. In addition, a comprehensive set of behavioral, life history, and annual fitness parameters have been recorded for nearly all individuals, providing important opportunities for assessing changes in social behavior. The lack of interisland dispersal (Komdeur et al. 2004a), combined with sampling of the entire population, provides a rare opportunity to monitor the survival, reproduction, and lifetime fitness of all individuals within the population. Our long-term research program into cooperative breeding, hand-in-hand with conservation actions, has created an experimental system in which we can attempt to unravel the factors that alter the cost-benefit trade-offs of cooperative breeding. Over time, this system has become proof of the power of the experimental methods and of the corrective value of long-term studies, where iterative examination with longer-term data sheds new insights on short-term findings. Here we detail various findings that have allowed us to uncover how changing social and ecological factors influence the form and function of reproductive competition and cooperation in the Seychelles warbler. We also outline how molecular genetic tools have given us a better understanding of the species’ cooperative breeding system and the selective factors that favor switching between different forms of cooperative and independent breeding

Temporal Variability and cooperative Breeding: Testing the Bet-Hedging Hypothesis in the Acorn Woodpecker

Cooperative breeding is generally considered an adaptation to ecological constraints on dispersal and independent breeding, usually due to limited breeding opportunities. Although benefits of cooperative breeding are typically thought of in terms of increased mean reproductive success, it has recently been proposed that this phenomenonmay be a bet-hedging strategy that reduces variance in reproductive success (fecundity variance) inpopulations living inhighly variable environments. We tested this hypothesis using long-term data on the polygynandrous acorn woodpecker (Melanerpes formicivorus). In general, fecundity variance decreased with increasing sociality, at least when controlling for annual variation in ecological conditions. Nonetheless, decreased fecundity variance was insufficient to compensate for reduced per capita reproductive success of larger,more social groups, which typically suffered lower estimatedmean fitness.We did, however, find evidence that sociality in the form of larger group size resulted in increased fitness in years following a small acorn crop due to reduced fecundity variance. Bet-hedging, although not the factor driving sociality in general, may play a role in driving acorn woodpecker group living when acorns are scarce and ecological conditions are poor

Brooding, Provisioning, and Compensatory Care in the Cooperatively Breeding Acorn Woodpecker

We analyzed reproductive investment in parental care (brooding and the provisioning of nestlings) in the acorn woodpecker (Melanerpes formicivorus), a cooperatively breeding species in which both polygynandry and helping-at-the-nest are common. As predicted based on the strategies pursued by birds of different sex and status, breeders generally invested more in parental care than helpers, and breeder females invested more than breeder males. Contrary to expectations, however, the degree to which individuals reduced their effort with increasing group size (i.e., patterns of load lightening or compensatory care) did not match overall investment. Instead, as group size increased, there was no significant difference in compensation in either brooding or provisioning among the different categories of birds. Compensation, at least by breeders, was significantly lower during the first week of the nestling period than later on, supporting the hypothesis that compensatory reduction in care is less likely when brood reduction is more common and was not affected by the acorn crop, which had no significant effect on the incidence of brood reduction despite being important to overall reproductive success. Our results offer support for the hypothesis that levels of compensation are influenced by the relative importance of brood reduction. More theoretical work, however, will be needed in order to understand the basis for patterns of compensation among individuals of different sex and status

New Mexico Daily Lobo, Volume 088, No 131, 4/9/1984

New Mexico Daily Lobo, Volume 088, No 131, 4/9/1984https://digitalrepository.unm.edu/daily_lobo_1984/1056/thumbnail.jp

Comparative reproductive success of Yellow-shafted, Red-shafted, and Hybrid Flickers across a hybrid zone

Alternative hypotheses of hybrid zones make specific predictions about reproductive components of fitness in the hybrids. The dynamic-equilibrium and reinforcement hypotheses are premised on reduced hybrid fitness, which should be apparent as reduced clutch or brood size or as increased embryonic mortality. The hybrid-superiority and introgression hypotheses predict normal clutch and brood size and embryonic mortality. Reproductive success was measured at four study sites on a transect across the hybrid zone between the Yellow- (Colaptes auratus auratus) and Red-shafted (C. a. cafer) subspecies of the Northern Flicker. Two additional clutch size samples representing pure Yellow- and Redshafted flickers were obtained from museum egg collections. Mean clutch size did not differ significantly among the six samples. Factorial ANOVAs showed that early clutches and broods are larger than late clutches and broods, but no significant difference was detected between hybrid and parental study sites. Analyses of the effect of phenotype (yellow-shafted, red-shafted, hybrid) also suggest that neither clutch size nor brood size is affected, with the exception that hybrid males sired significantly smaller broods. Finally, there were no significant effects of type of cross (red-shafted male x hybrid female, etc.) on the ratio broodsize / clutch-size. The only evidence for reduced hybrid fitness was in the test where males with hybrid phenotypes appear to have sired small broods. This may indicate that abnormal behavior of hybrid males affects female fecundity, but it is also plausible that this marginally significant result is a type I statistical error. The overall lack of evidence for reduced hybrid fitness is inconsistent with either the dynamic-equilibrium or reinforcement models. Of the two remaining alternatives, the bounded hybrid-superiority model appears the more likely explanation of the Northern Flicker hybrid zone because earlier work (Moore and Buchanan 1985) showed that the hybrid zone is not becoming broader, as predicted by the introgression model

Star Formation and Young Population of the HII Complex Sh2-294

The Sh2-294 HII region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in the region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 HII region at 3.6, 4.5, 5.8, and 8.0 microns observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H2 (2.12 microns) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the HII region and associated with enhanced H2 emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (< 4 solar masses) YSOs; however, we also detected a massive YSO (~9 solar masses) of Class I nature, embedded in a cloud of visual extinction of ~24 mag. Present analysis suggests that the Class I sources are indeed younger population of the region relative to Class II sources (age ~ 4.5 x 10^6 yr). We suggest that the majority of the Class I sources, including the massive YSOs, are second-generation stars of the region whose formation is possibly induced by the expansion of the HII region powered by a ~ 4 x 10^6 yr B0 main-sequence star.Comment: 12 pages, 7 figures, 2 tables. Accepted for publication in The Astrophysical Journa