Annette Aiello

INFERENCES FROM A RAPIDLY MOVING HYBRID ZONE

Abstract Anartia fatima and Anartia amathea (Lepidoptera: Nymphalidae) are sister taxa whose ranges abut in a narrow hybrid zone in eastern Panama. At the center of the zone, hybrids are abundant, although deviations from Hardy‐Weinberg and linkage disequilibria are strong, due in part to assortative mating. We measured differences across the zone in four wing color‐pattern characters, three allozyme loci, and mitochondrial haplotype. Wing pattern, allozyme, and mitochondrial clines were coincident (i.e., had the same positions) and concordant (i.e., all markers had similar cline shapes, about 28 km wide). Repeated samples demonstrated that the hybrid zone has been moving eastwards at an average rate of 2.5 km/year over the past 20 years, accompanied by an equivalent movement of the mtDNA cline. No introgression of mtDNA haplotypes were found in the “wake” of the moving cline, as might be expected for a neutral marker. The concordance of morphological and mtDNA clines between 1994 and 2000, in spite of hybrid zone movement, suggests strong epistasis between the mitochondrial genome and nuclear loci. Cline movement is achieved mainly by pure fatima immigrating into amathea populations; hybrids had little effect, and were presumably outcompeted by fitter pure fatima genotypes. This movement can be explained if random dispersal of 7–19 km.gen∼1/2 is coupled with a competitive advantage to A. fatima genomes of 2–5%. Hybrid zone motion is equivalent to Phase III of Wrights shifting balance. Hybrid zone movement has rarely been considered likely in the past, but our results show that it may be more important in biogeography and evolution than generally realized.

General herbivore outbreak following an El Niño-related drought in a lowland Panamanian forest

A severe outbreak of Lepidoptera followed the 1997-98 El Ni ˜ no Southern Oscillation event, during which the climate in central Panama was unusually dry. The outbreak involved the larvae of at least 12 species of Lepidoptera and occurred at a seasonally dry, deciduous forest site, where extensive background data were available regarding climate, tree species and non-outbreak herbivory levels. Most Lepidoptera were associated with only one or two larval host plant species belonging to the same family, and the majority were monophagous during this study. During the outbreak, caterpillar densities for the major outbreak species averaged 1.6 larvae per young leaf and 0.18 larvae per leaf for leaves of all ages. For canopy trees and lianas, the mean level of leaf damage was 13.8%, ranging from 1-100%. Seven out of 20 tree species sustained most of the damage, with 21-37% of the leaf area consumed. Relative to non-outbreak years, damage levels increased by more than 250% during the outbreak. Single-species outbreaks were observed in other areas with a similar drought, but wetter forests in central Panama did not experience outbreaks during this period. Historically, fewer outbreaks have been reported from tropical forests than from temperate forests, however, similar El Ni ˜ no-related outbreaks have occurred recently in several other locations throughout the tropics.

Speciation in two neotropical butterflies: extending Haldane's rule

Anartia fatima and A. amathea form a hybrid zone in Panama where F1 and back–cross hybrids are found. Crosses were carried out to determine the nature of any reproductive isolation between these two butterflies. A novel analysis demonstrated both strong assortative mating among the pure forms and an unusual example of Haldanes rule: F1 hybrid females (the heterogametic sex) from the cross A. amathea (female) multiplied by A. fatima (male) have a reduced tendency to mate. Historically, Haldanes rule has been restricted to hybrid mortality or sterility and most studies have concentrated on taxa (predominantly Drosophila) between which strong barriers to gene flow already exist. Our data suggest that Haldanes rule might be extended to cover any decrease in hybrid fitness and that mating propensity may provide a sensitive and comparable means of assessing such decreases. Other barriers to gene flow were also evident in Anartia: F1 hybrid females have reduced fertility (also a Haldane effect) and larval survivorship was greatly reduced in F2 hybrids of both sexes. These examples of hybrid disruption are expected under the dominance theory of Haldanes rule but do not exclude other explanations.

Molecular evidence for a diverse green algal community growing in the hair of sloths and a specific association with Trichophilus welckeri (Chlorophyta, Ulvophyceae).

BackgroundSloths are slow-moving arboreal mammals inhabiting tropical rainforests in Central and South America. The six living species of sloths are occasionally reported to display a greenish discoloration of their pelage. Trichophilus welckeri, a green algal species first described more than a century ago, is widely believed to discolor the animals fur and provide the sloth with effective camouflage. However, this phenomenon has not been explored in any detail and there is little evidence to substantiate this widely held opinion.ResultsHere we investigate the genetic diversity of the eukaryotic community present in fur of all six extant species of sloth. Analysis of 71 sloth hair samples yielding 426 partial 18S rRNA gene sequences demonstrates a diverse eukaryotic microbial assemblage. Phylogenetic analysis reveals that sloth fur hosts a number of green algal species and suggests that acquisition of these organisms from the surrounding rainforest plays an important role in the discoloration of sloth fur. However, an alga corresponding to the morphological description of Trichophilus welckeri was found to be frequent and abundant on sloth fur. Phylogenetic analysis demonstrated the retention of this alga on the fur of sloths independent of geographic location.ConclusionsThese results demonstrate a unique diverse microbial eukaryotic community in the fur of sloths from Central and South America. Our analysis streghtens the case for symbiosis between sloths and Trichophilus welckeri.

Disruptive Coloration in Butterflies: Lack of Support in Anartia fatima

Experimental obliteration of high-contrast wing stripes of the neotropical butterfly Anartia fatima affected neither survival nor wing damage in a natural population over a 5-month period. There is no direct evidence supporting the hypothesis that so-called disruptive wing patterns function as protective coloration in butterflies.

Neotropical Butterflies of the Genus Anartia: Systematics, Life Histories, and General Biology (Lepidoptera: Nymphalidae)

Butterflies of the genus Anartia Hiibner are among the most common and conspicuous diurnal Lepidoptera encountered in the New World tropics. While their abundance and ease of capture have made them popular subjects for research in various aspects of lepidopteran biology, the genus has never been thoroughly reviewed or revised. Two of the authors, (R.E.S. and A.A.) have been conducting genetic, behavioral and ecological experiments on members of this genus for four years, and we feel it is both an opportunity and a necessity to condense the scattered published information with some of our own observations and results. Our experimental findings will be published separately. As treated here, Anartia consists of five species (Figure 1) in three well-defined groups (Godman and Salvin, 1882).

Ecological and evolutionary bioprospecting: using aposematic insects as guides to rainforest plants active against disease

We examined Coleoptera and Lepidoptera assemblages feeding on two different groups of plants: one in which plants were active against cancer cell lines and/or protozoan parasites responsible for tropical parasitic diseases, and a second group that was inactive in the same bioassays. Aposematic species were found on nine of the ten active plant species, but on only four of the ten inactive plant species. Non-aposematic insects did not show a significant difference in their association with active versus inactive plants. Our results suggest that the presence of aposematic, herbivorous insects can be used to facilitate the identification of plants with compounds active against important human diseases.

Keeping the band together: evidence for false boundary disruptive coloration in a butterfly

There is a recent surge of evidence supporting disruptive coloration, in which patterns break up the animals outline through false edges or boundaries, increasing survival in animals by reducing predator detection and/or preventing recognition. Although research has demonstrated that false edges are successful for reducing predation of prey, research into the role of internal false boundaries (i.e. stripes and bands) in reducing predation remains warranted. Many animals have stripes and bands that may function disruptively. Here, we test the possible disruptive function of wing band patterning in a butterfly, Anartia fatima, using artificial paper and plasticine models in Panama. We manipulated the band so that one model type had the band shifted to the wing margin (nondisruptive treatment) and another model had a discontinuous band located on the wing margin (discontinuous edge treatment). We kept the natural wing pattern to represent the false boundary treatment. Across all treatment groups, we standardized the area of colour and used avian visual models to confirm a match between manipulated and natural wing colours. False boundary models had higher survival than either the discontinuous edge model or the nondisruptive model. There was no survival difference between the discontinuous edge model and the nondisruptive model. Our results demonstrate the importance of wing bands in reducing predation on butterflies and show that markings set in from the wing margin can reduce predation more effectively than marginal bands and discontinuous marginal patterns. This study demonstrates an adaptive benefit of having stripes and bands.

Moth-like butterflies (Hedylidae: Lepidoptera): a summary, with comments on the egg

Our concept of the butterflies (Hesperioidea or skippers plus Papilionoidea or true butterflies) has been broadened by the inclusion of the Hedylidae (Scoble, 1986), a group of about 40 species of Neotropical Lepipdoptera. Superficially moth-like as adults, hedylids exhibit several specialized characters associated with various families of butterflies. They may have diverged little from the unknown ancestors of true butterflies. The butterfly-like characters of all stages in the life history are summarized; particular note is made of the egg.

The Butterflies of Barro Colorado Island, Panama: Local Extinction since the 1930s

Few data are available about the regional or local extinction of tropical butterfly species. When confirmed, local extinction was often due to the loss of host-plant species. We used published lists and recent monitoring programs to evaluate changes in butterfly composition on Barro Colorado Island (BCI, Panama) between an old (1923–1943) and a recent (1993–2013) period. Although 601 butterfly species have been recorded from BCI during the 1923–2013 period, we estimate that 390 species are currently breeding on the island, including 34 cryptic species, currently only known by their DNA Barcode Index Number. Twenty-three butterfly species that were considered abundant during the old period could not be collected during the recent period, despite a much higher sampling effort in recent times. We consider these species locally extinct from BCI and they conservatively represent 6% of the estimated local pool of resident species. Extinct species represent distant phylogenetic branches and several families. The butterfly traits most likely to influence the probability of extinction were host growth form, wing size and host specificity, independently of the phylogenetic relationships among butterfly species. On BCI, most likely candidates for extinction were small hesperiids feeding on herbs (35% of extinct species). However, contrary to our working hypothesis, extinction of these species on BCI cannot be attributed to loss of host plants. In most cases these host plants remain extant, but they probably subsist at lower or more fragmented densities. Coupled with low dispersal power, this reduced availability of host plants has probably caused the local extinction of some butterfly species. Many more bird than butterfly species have been lost from BCI recently, confirming that small preserves may be far more effective at conserving invertebrates than vertebrates and, therefore, should not necessarily be neglected from a conservation viewpoint.