Cardenolide content of Danaus chrysippus butterflies from three areas of East Africa

The African butterfly Danaus chrysippus , like other members of the family Danaidae, feeds as a larva on species of milkweeds (Asclepiadaceae). It has been demonstrated in a sample from a West African population that only a minority of adult D. chrysippus accumulated detectable amounts of poisonous and presumably emetic cardenolides from their larval foodplants. It has also been shown in D. chrysippus and the related monarch butterfly ( D. plexippus ) that the cardenolide content of adults varies with that of their respective milkweed foodplants.
Three population samples of D. chrysippus from sites in East Africa are analysed for cardenolides using the spectrophotometric technique refined by Brower, Edmunds & Moffitt (1975), which allows the assay of individual butterflies. The East African samples all have a palatability spectrum with a considerably higher percentage of cardenolide-containing individuals than the West African one.
This is discussed in terms of its effect on potential bird predators and the 'automimicry' of emetic by palatable individuals. In East Africa D. chrysippus is polymorphic and appears to act as a model in a complex mimicry ring, whereas in West Africa it is monomorphic and may have 'shed' most of its mimics. This latter hypothesis is discussed in the light of our results.     

Monarch butterfly host plant (milkweed Asclepias spp.) abundance varies by habitat type across 98 prairies

The decline in migratory monarch butterflies (Danaus plexippus) over the past 20 years has been attributed to several drivers, including loss of their host plants (milkweeds Asclepias spp.). This has sparked widespread interest in milkweed ecology and restoration. We developed a model on environmental and habitat‐type variables to predict milkweed abundance by sampling 93 prairie plantings (47 conservation plantings and 46 roadsides) and 5 unplowed prairie remnants throughout the state of Iowa, United States. Milkweeds were censused in 10–25 random locations within each site, and data on plant diversity, age of planting, soil characteristics, and management were tested as predictors of abundance. Milkweed densities of all species combined were highest in remnant prairies (8,705 stems/ha), intermediate in roadside plantings (1,274 stems/ha), and lowest in conservation plantings (212 stems/ha). Most milkweeds were common milkweeds Asclepias syriaca, which were more abundant in roadside than conservation plantings. Remnants contained the most milkweed species. Total milkweed and common milkweed abundance were both predicted by higher soil pH, a more linear site shape, and lower soil bulk density across restorations. Our results indicate that common milkweed is maintained by disturbance, and establishes readily in rural roadside habitat. Remnants are important as reservoirs for multiple milkweed species and should be protected.     

Climate, life forms and species distribution on the Loma Montane grassland, Sierra Leone

The Loma Mountains (2090 m), situated in lowland south Guinea savanna in Sierra Leone, are shown to have a cooler and more mesic climate than the savanna region. A temperature lapse rate of 7.5^o C/1000 m is calculated using means for the dry, dry/wet, wet and wet/dry seasons of the year. In the montane grassland the life forms of the species are predominantly hemicryptophytic, and the biological spectrum is closer to that of temperate grasslands than to the savanna type, although the adverse conditions are still dry-season drought and fires. The phytogeographical distribution of the flora indicates a 44% widespread, truly montane to montane/savanna element and a 43% West African endemic element. In the Guinean highlands, the Loma/Tingi group shows about 10% disjunction of its grassland flora with other African mountains outside West Africa.     

Systematic revision of the genus Aglyptodactylus Boulenger, 1919 (Amphibia: Ranidae), and analysis of its phylogenetic relationships to other Madagascan ranid genera (Tomopterna, Boophis, Mantidactylus, and Mantella)

Recent field studies revealed two new species of the genus Aglyptodactylus (Amphibia: Anura: Ranidae), which was hitherto considered as monotypic and confined to humid eastern Madagascar. Both new species, Aglyptodactylus laticeps sp. n. and Aglyptodactylus securifer sp. n. , occur syntopically in the deciduous dry forest of Kirindy in western Madagascar. In comparison to Aglyptodactylus madagascariensis from eastern rainforests, the new species A. laticeps shows a remarkable morphological divergence, which may be partly due to adaptations to burrowing habits in dry environments. Despite of the morphological differentiation, advertisement calls and osteology indicate that all three species of Aglyptodactylus are closely related. A phylogenetic analysis of the Madagascan ranid genera Aglyptodactylus, Mantella, Mantidactylus, Boophis , and Tomopterna (the latter including species from Madagascar, Africa, and Asia) strongly supports a sister group relationship of Aglyptodactylus with the ranine genus Tomopterna . We therefore transfer Aglyptodactylus from the Rhacophorinae to the Raninae and discuss implications of this rearrangement for ranoid systematics. The existence of the endemic genus Aglyptodactylus in Madagascar as well as its close phylogenetic relationships to Tomopterna confirm that the Raninae were already present on the Madagascan plate before its separation from Africa. The Madagascan Tomopterna labrosa shows several important differences both to Asian and to African species of the genus, and is therefore transferred from the subgenus Sphaerotheca (now restricted to Asia) to a new subgenus Laliostoma subgen. n .     

Implications of global warming for the climate of African rainforests

African rainforests are likely to be vulnerable to changes in temperature and precipitation, yet there has been relatively little research to suggest how the regional climate might respond to global warming. This study presents projections of temperature and precipitation indices of relevance to African rainforests, using global climate model experiments to identify local change as a function of global temperature increase. A multi-model ensemble and two perturbed physics ensembles are used, one with over 100 members. In the east of the Congo Basin, most models (92%) show a wet signal, whereas in west equatorial Africa, the majority (73%) project an increase in dry season water deficits. This drying is amplified as global temperature increases, and in over half of coupled models by greater than 3% per °C of global warming. Analysis of atmospheric dynamics in a subset of models suggests that this could be partly because of a rearrangement of zonal circulation, with enhanced convection in the Indian Ocean and anomalous subsidence over west equatorial Africa, the Atlantic Ocean and, in some seasons, the Amazon Basin. Further research to assess the plausibility of this and other mechanisms is important, given the potential implications of drying in these rainforest regions.     

The phylogeny of the Pantropical genus Arrhipis Bonvouloir (Coleoptera, Eucnemidae)

The phylogeny of the genus Arrhipis Bonvouloir (Coleoptera, Eucnemidae) is clarified with a cladistic analysis based on five molecular markers and morphology. Sixteen species from Africa, America, Asia, and Australia are included in the analysis. Two separate Asian clades are recovered, one of them being the sister group to a clade with the American and African species. With the exception of the continental south-east Asian species, all Gondwanan regions have monophyletic faunas. According to the present data, the continental south-east Asian fauna comprises two monophyletic groups, one of which is the sister group to African and American species. Vicariance seems to be the logical explanation for the distribution of these lignicolous beetles.
© The Willi Hennig Society 2009.     

African rainforests: past,present and future

The rainforests are the great green heart of Africa, and present a unique combination of ecological, climatic and human interactions. In this synthesis paper, we review the past and present state processes of change in African rainforests, and explore the challenges and opportunities for maintaining a viable future for these biomes. We draw in particular on the insights and new analyses emerging from the Theme Issue on ‘African rainforests: past, present and future’ of Philosophical Transactions of the Royal Society B. A combination of features characterize the African rainforest biome, including a history of climate variation; forest expansion and retreat; a long history of human interaction with the biome; a relatively low plant species diversity but large tree biomass; a historically exceptionally high animal biomass that is now being severely hunted down; the dominance of selective logging; small-scale farming and bushmeat hunting as the major forms of direct human pressure; and, in Central Africa, the particular context of mineral- and oil-driven economies that have resulted in unusually low rates of deforestation and agricultural activity. We conclude by discussing how this combination of factors influences the prospects for African forests in the twenty-first century.     

Colonization and usage of eight milkweed (<Emphasis Type="Italic">Asclepias</Emphasis>) species by monarch butterflies and bees in urban garden settings

Planting milkweeds on public and private lands has emerged as a central conservation strategy for restoring declining North American migratory populations of the monarch butterfly (Danaus plexippus). Nearly all actionable science on this issue has focused on restoring common milkweed (Asclepias syriaca L.) in rural land types. The aim of this study was to develop recommendations for the best milkweeds for managed gardens intended to support both monarch butterflies and bees. Eight milkweed (Asclepias) species varying in height, form, and leaf shape were grown in a common-garden experiment at a public arboretum. We measured milkweed growth, tillering, and bloom periods, conducted bi-weekly counts of eggs and larvae to assess colonization by wild monarchs, and evaluated suitability for growth of monarch larvae. We also quantified bee visitation and compared the bee assemblages associated with six of the eight species, augmented with additional collections from other sites. Monarchs rapidly colonized the gardens, but did not equally use all of the milkweed species. More eggs and larvae were found on taller, broad-leaved milkweeds, but there was relatively little difference in larval performance, suggesting ovipositional preference for more apparent plants. Asclepias tuberosa and A. fascicularis attracted the greatest number of bees, whereas bee genus diversity was greatest on A. verticillata, A. fascicularis, and A. tuberosa. Milkweeds that do not spread extensively by tillering may be best suited for managed gardens. Combining milkweeds that are preferred by ovipositing monarchs with ones that are particularly attractive to bees may enhance conservation value of small urban gardens.     

Can roadside habitat lead monarchs on a route to recovery?

The Eastern North American monarch butterfly population has severely declined over the past decade. The decreasing availability of larval host plants (milkweeds) due to the use of herbicide-tolerant crops has been implicated in this decline. Roadsides could provide additional habitat for monarchs. In this study we document the occurrence of milkweed and monarchs on roadsides, and discuss whether roadsides are appropriate targets for monarch habitat restoration. We sampled roadside rights-of-way in the Upper Midwestern U.S. during the summer of 2015 to estimate the abundance, distribution, and diversity of milkweeds and the extent to which monarchs use these milkweeds. We then compared monarch densities in roadsides to other habitat types and modelled immature monarch densities based on several site characteristics. Our findings suggest that roadsides have conservation potential for monarchs, especially when other habitat is scarce and if wildlife-friendly management practices are enacted. Milkweeds were found on ~60% of roadside transects. Asclepias syriaca was the most common of the seven species encountered, occurring on 97% of transects with milkweed. Immature monarchs were observed in roadsides, but in lower densities than other habitats during the same time period. At lower milkweed densities, immature monarch density per unit area is positively correlated with milkweed density. However, milkweed density weakens as a predictor of immature monarch density over ~0.6 plants per m², possibly indicating a saturation effect.     

The taxonomy and systematics of Apocynaceae: where we stand in 2012

In their most recent classification of Apocynaceae in 2000, Endress and Bruyns recognized five subfamilies of Apocynaceae (Rauvolfioideae, Apocynoideae, Periplocoideae, Secamonoideae and Asclepiadoideae). Subsequently, through various studies using molecular data, it has been shown that most tribes and subtribes of Rauvolfioideae were not monophyletic, and new tribes and subtribes have been erected to reflect improved phylogenetic understanding of the family: Aspidospermeae in Rauvolfioideae; Nerieae, Odontadenieae and Baisseeae in Apocynoideae; Fockeeae in Asclepiadoideae; and Orthosiinae in Asclepiadeae. Several genera in Rauvolfioideae have been reassigned to different tribes in order to improve the monophyly of these tribes. The sister group of Asclepiadoideae plus Secamonoideae is not Periplocoideae, as formerly assumed, but tribe Baisseeae. Periplocoideae are nested in Apocynoideae. However, tribal composition remains unclear in some parts of the family. Clade structure in Apocynaceae is now generally well understood. The principal challenges now lie in identifying characters that can reflect and articulate these clades in a formal classification. Species‐rich, recent radiations such as core Asclepiadinae in Africa and the Metastematinae in Latin America present particular problems in this regard. © 2013 The Linnean Society of London     

Aggregation and Mate Location in the Red Milkweed Beetle (Coleoptera: Cerambycidae)

We examined behavioral mechanisms underlying aggregation and mate location in the red milkweed beetle, Tetraopes tetrophthalmus (Forster) (Coleoptera: Cerambycidae). Larvae of this species feed on rhizomes of common milkweed, Asclepias syriaca L., and adults feed on the flowers and foliage, aggregating on individual stems within milkweed patches. Adults preferred to aggregate on milkweeds that had multiple, large inflorescences. Males actively searched for females, often flying between host plants. Mate location did not appear to involve long-range pheromones or vision, but rather males landed on milkweed stems arbitrarily, whether or not females were present. Males remained for longer periods, and so tended to accumulate, on milkweed stems that had female-biased sex ratios. We conclude that aggregation of T. tetrophthalmus is cued by host plant characteristics but dynamically influenced by the sex ratio of conspecifics present on individual stems.     

Spatial patterns and recent trends in the climate of tropical rainforest regions

We present an analysis of the mean climate and climatic trends of tropical rainforest regions over the period 1960-1998, with the aid of explicit maps of forest cover and climatological databases. Until the mid-1970s most regions showed little trend in temperature, and the western Amazon experienced a net cooling probably associated with an interdecadal oscillation. Since the mid-1970s, all tropical rainforest regions have experienced a strong warming at a mean rate of 0.26 +/- 0.05 degrees C per decade, in synchrony with a global rise in temperature that has been attributed to the anthropogenic greenhouse effect. Over the study period, precipitation appears to have declined in tropical rainforest regions at a rate of 1.0 +/- 0.8% per decade (p < 5%), declining sharply in northern tropical Africa (at 3-4% per decade), declining marginally in tropical Asia and showing no significant trend in Amazonia. There is no evidence so far of a decline in precipitation in eastern Amazonia, a region thought vulnerable to climate-change-induced drying. The strong drying trend in Africa suggests that this should be a priority study region for understanding the impact of drought on tropical rainforests. We develop and use a dry-season index to study variations in the length and intensity of the dry season. Only African and Indian tropical rainforests appear to have seen a significant increase in dry-season intensity. In terms of interannual variability, the El Niño-Southern Oscillation (ENSO) is the primary driver of temperature variations across the tropics and of precipitation fluctuations for large areas of the Americas and southeast Asia. The relation between ENSO and tropical African precipitation appears less direct.     

A 37,500-year pollen record from Lake Malaŵi and implications for the biogeography of afromontane forests

Abstract. Two 10-metre cores were analysed and a 37,500 year pollen stratigraphy was established for Lake Mala?i. A lowstand from 37,500 to 35,900 BP indicates extremely dry conditions. From 35,900 to 34,000 BP montane forests were widespread indicating cold, moist climate. Between 34,000 and 26,400 BP warm and dry conditions prevailed and forest area decreased. During the Last Glacial Maximum montane forest was widespread in the catchment, although woodlands apparently persisted at low altitudes: the expansion of the montane forest indicates that the aridity that affected equatorial Africa during this time period did not affect the Lake Mala?i Catchment. The cold and relatively moist conditions during the Late Pleistocene probably allowed biotic interchange between the highlands of East and West Africa via the highlands along the Zaire—Zambezi watershed and among now-isolated islands of Afromontane vegetation in the Lake Mala?i catchment. The Holocene is characterized by climate and vegetation quite similar to today, with indications of slightly wetter conditions between 6150 and 3000 bp and slightly drier conditions between 8000 and 6150 bp . The low percentages of montane forest pollen throughout the Holocene support the hypothesis that the montane grasslands of Mala?i are not recently anthropogenic.     

Interrogating recent range changes in South African birds: confounding signals from land use and climate change present a challenge for attribution

Aim Apparent anthropogenic warming has been underway in South Africa for several decades, a period over which significant range shifts have been observed in some indigenous bird species. We asked whether these range shifts by birds are clearly consistent with either climate change or land use change being the primary driver. Location South Africa. Methods We categorized recent range changes among 408 South African terrestrial bird species and, using generalized linear mixed models, analysed ecological attributes of those species that have and have not changed their ranges. Results Fifty‐six of the 408 taxa studied have undergone significant range shifts. Most extended their ranges towards the south (towards cooler latitudes, consistent with climate‐change drivers) or west (towards drier and warmer habitats, inconsistent with climate drivers but consistent with land use drivers); very few moved east or north. Both southward and westward movers were habitat generalists. Furthermore, southward movers were mobile taxa (migrants and nomads), whereas westward movers were associated with human‐modified elements in the landscape, such as croplands, plantations or buildings. Main conclusions The results suggest that both land use changes and climate change may simultaneously be influencing dynamic range shifts by South African birds, but separating the relative strengths of these two drivers is challenging, not least because both are operating concurrently and may influence some species simultaneously. Those species that respond to land use change by contracting their ranges are likely to be among the species that will be most impacted by climate change if land use practices with negative impacts are occurring in areas anticipated to become climatic refugia for these species. This highlights a pressing need to develop dynamic models of species’ potential range shifts and changing abundances that incorporate population and dispersal processes, as well as ecological processes that influence habitat suitability.     

Millennium-Scale Crossdating and Inter-Annual Climate Sensitivities of Standing California Redwoods

Extremely decay-resistant wood and fire-resistant bark allow California’s redwoods to accumulate millennia of annual growth rings that can be useful in biological research. Whereas tree rings of Sequoiadendron giganteum (SEGI) helped formalize the study of dendrochronology and the principle of crossdating, those of Sequoia sempervirens (SESE) have proven much more difficult to decipher, greatly limiting dendroclimatic and other investigations of this species. We overcame these problems by climbing standing trees and coring trunks at multiple heights in 14 old-growth forest locations across California. Overall, we sampled 1,466 series with 483,712 annual rings from 120 trees and were able to crossdate 83% of SESE compared to 99% of SEGI rings. Standard and residual tree-ring chronologies spanning up to 1,685 years for SESE and 1,538 years for SEGI were created for each location to evaluate crossdating and to examine correlations between annual growth and climate. We used monthly values of temperature, precipitation, and drought severity as well as summer cloudiness to quantify potential drivers of inter-annual growth variation over century-long time series at each location. SESE chronologies exhibited a latitudinal gradient of climate sensitivities, contrasting cooler northern rainforests and warmer, drier southern forests. Radial growth increased with decreasing summer cloudiness in northern rainforests and a central SESE location. The strongest dendroclimatic relationship occurred in our southernmost SESE location, where radial growth correlated negatively with dry summer conditions and exhibited responses to historic fires. SEGI chronologies showed negative correlations with June temperature and positive correlations with previous October precipitation. More work is needed to understand quantitative relationships between SEGI radial growth and moisture availability, particularly snowmelt. Tree-ring chronologies developed here for both redwood species have numerous scientific applications, including determination of tree ages, accurate dating of fire-return intervals, archaeology, analyses of stable isotopes, long-term climate reconstructions, and quantifying rates of carbon sequestration.     

中国北方黄土地层中的哺乳动物群及在磁性地层中的位置

本文研究了中国黄土地层中有确切层位的哺乳动物化石记录,并进行了生物地层学与磁性地层学对比,将黄土地层中的动物化石归纳成如下哺乳动物群：早更新世（2．50─0．73Ma）：午城动物群（2．50─1．20Ma）、公王岭动物群（1．20─1．10Ma）和阳郭动物群（1．10─0．90Ma）、中更新世（0．73─0．13Ma）：陈家窝子动物群（0．73─0．40Ma）;晚更新世（0．13─0．01Ma）：柔远─靖远动物群（0．13─0．01Ma）;全新世（0．01Ma─Rec）:半坡动物群。结果表明：早更新世许多森林习性的化石动物虽然反映出气候较第三纪的寒冷,但比后期温暖湿润。中更新世出现了较多的草原、干旱草原习性的动物,气候更为寒冷干旱,森林逐渐减少或消失,草原或干旱草原得到发展;晚更新世出现的沙鼠、跳鼠等动物,表明气候更加寒冷、干旱,部分地区甚至沙化。     

Monarchs in decline: a collateral landscape‐level effect of modern agriculture

We review the postulated threatening processes that may have affected the decline in the eastern population of the monarch butterfly, Danaus plexippus L. (Lepidoptera: Nymphalidae), in North America. Although there are likely multiple contributing factors, such as climate and resource‐related effects on breeding, migrating, and overwintering populations, the key landscape‐level change appears to be associated with the widespread use of genetically modified herbicide resistant crops that have rapidly come to dominate the extensive core summer breeding range. We dismiss misinterpretations of the apparent lack of population change in summer adult count data as logically flawed. Glyphosate‐tolerant soybean and maize have enabled the extensive use of this herbicide, generating widespread losses of milkweed (Asclepias spp.), the only host plants for monarch larvae. Modeling studies that simulate lifetime realized fecundity at a landscape scale, direct counts of milkweeds, and extensive citizen science data across the breeding range suggest that a herbicide‐induced, landscape‐level reduction in milkweed has precipitated the decline in monarchs. A recovery will likely require a monumental effort for the re‐establishment of milkweed resources at a commensurate landscape scale.     

The effect of host plant phenology on reproduction of the milkweed bug,Oncopeltus fasciatus,in tropical Florida

Summary A field study of the relationship between host plant phenology and the reproductive pattern of the large milkweed bug, Oncopeltus fasciatus, was conducted in south Florida. Since O. fasciatus need seeds of either milkweed or Nerium oleander plants to reproduce, reproduction takes place on only those host plants that are producing seed pods.Two of four major host plants, Asclepias incarnata and Sarcostemma clausa fruit seasonally, producing pods in early autumn and early winter, respectively. The third milkweed host, Asclepias curassavica, produces almost no pods midsummer (although it flowers abundantly) and few pods midwinter. Nerium oleander (Apocynaceae) produces some pods all year but is only used by O. fasciatus in the summer when milkweeds are not producing pods. Correspondingly, reproduction of O. fasciatus has been observed year round, but relatively few females reproduce in midwinter, coinciding with decreased pod production and low temperatures. This pattern is consistent with the hypothesis that a photoperiodic cue of short day lengths under conditions of cool temperatures may cause adult females to enter diapause and delay reproduction in the field.A comparison of plant phenologies and rainfall between 1976, a very dry year, and 1978, a year with normal rainfall, showed that extreme dryness disrupted the seasonal fruiting of the milkweeds and consequently the reproduction of O. fasciatus.     

An Insight into Paleovegetation on the Emerged Shelf at the Last Glaciation: Pollen Date of the South China Sea

Vegetation on the emerged continental shelves of the South China Sea (SCS) during the Last Glacial Maximum (LGM) was deduced based on pollen of hemipelagic sediments from the continental slopes and the consideration of pollen transport dynamics and source areas. During the LGM (including the top of Oxygen Isotope Stage 3) the sea level might be more than 100 m lower than that of the present. Consequently, both northern and southern continental shelves of the SCS were exposed. The northern continental shelf was covered by grassland mainly of Artem/s/a. The climate should be cold and dry, whereas on the southern continental shelf (Sunda Land) was spread tropical lowland rainforest and mangroves were scattered by the river mouths and along the coast. The climate might be cooler than that in the present day, but drop of humidity was not observed.     

Out of Africa and into an ice age: on the role of global climate change in the late Pleistocene migration of early modern humans out of Africa

The results from two climate model simulations are used to explore the relationship between North Atlantic sea surface temperatures and the development of African aridity around 100,000 years ago. Through the use of illustrative simulations with an Earth System Climate Model, it is shown that freshwater fluxes associated with ice sheet surges into the North Atlantic, known as Heinrich events, lead to the southward shift of the intertropical convergence zone over Africa. This, combined with the overall increased aridity in the cooler mean climate, leads to substantial changes in simulated African vegetation cover, particularly in the Sahel. We suggest that Heinrich events, which occurred episodically throughout the last glacial cycle, led to abrupt changes in climate that may have rendered large parts of North, East, and West Africa unsuitable for hominin occupation, thus compelling early Homo sapiens to migrate out of Africa.