Tropical dry and wet season polyphenism in the butterfly Melanitis leda (Satyrinae): Phenotypic plasticity and climatic correlates

Changes in wing pattern, colour, shape and size associated with seasonal polyphenism in Melanitis leda were quantified using a series of 155 butterflies collected by N. Manders on Mauritius in 1905. Butterflies of the wetter period were predominantly of the wet season form with large, well differentiated eyespots, short tails, smaller wings and a characteristic background colour. The dry season form occurred only in the drier period and has much smaller eyespots, longer tails, larger wings and a variable background. Many intermediates occurred, mainly in the drier period. These are associated with an absence of extreme seasonal change in Mauritius. The first principal component (PCI) describing the morphometric and colour data is closely related to the wing form (r = 0.80). Regression analyses using temperature and rainfall data for the 8 weeks before each capture showed that about 40% of variation in PCI could be accounted for by temperature in weeks 2–3 before capture. Many of the characters measured are redundant; a subset of seven morphometric characters yields a closely similar PCI. Analysis of is subset in an additional sample of 70 M. leda from Kenya showed that the seasonal polyphenism overrides a small degree of sexual dimorphism. The results are discussed with regard to seasonal changes in adult activity, resting backgrounds and visual predation. Wing phenotype characters are part of an array of coordinated morphological and life history traits which include ovarian dormancy and fat body development in dry season adults. A partial independence occurs in the proximal control of these traits as indicated, for example, by the larger wing and tail size, and smaller eyespots of the small number of the wet season form captured in the drier period in comparison to those of the wetter months.     

Seasonal polyphenism in Bicyclus (Lepidoptera: Satyridae) butterflies: different climates need different cues

A comparison is made between northern and southern hemisphere populations of Bicyclus butterflies in Africa regarding their responses in wing pattern polyphenism to seasonal change in rainfall and temperature. In southern habitats where temperature and rainfall are often positively correlated, a high temperature during the larval period induces conspicuous wet season forms whereas a fall in temperature elicits cryptic dry season forms. In northern habitats, however, where temperature and rainfall usually are negatively correlated, a rise in temperature should not induce a wet season form because such a rise is correlated with the onset of the dry season. Here, wing pattern plasticity, as measured using museum material, was regressed on mean monthly values for rainfall and temperature. Rainfall appeared to be a frequent determinant of wing pattern plasticity whereas temperature was much less often a significant independent variate. We conclude that the wing pattern may only respond to seasonal change in temperature if rainfall and temperature are positively correlated; in other situations rainfall remains the only significant determinant for wing pattern plasticity.     

Reproductive seasonality in tropical satyrine butterflies: strategies for the dry season

Abstract.

• 1 In tropical savanna environments rainfall is often very seasonal, so that much of the year is characterized by a long and unpredictable dry season. Because the timing and availability of rain exerts a major influence on plant growth and production, many species during the dry period exhibit dramatic reduction in leaf quality. Accordingly, and kind of behaviour shown by phytophagous insects that synchronizes larval feeding with food availability will be adaptive.
• 2 The reproductive status of three Mycalesis butterflies was monitored over a 2-year period (1989–90) in north-eastern Queensland, Australia, at a lowland site (Cardwell, 18°16's, 146°02′E) which experiences a pronounced dry season. Females of these species and of five other satyrines (Ypthima, Hypocysta spp.) were also examined less intensively during the dry season in areas throughout northern and central Queensland, north of the tropic of Capricorn.
• 3 These relatively sedentary butterflies exhibit three different strategies for dealing with the unpredictable dry period and associated deterioration of larval food plants (grass). First, five species appear to breed continuously, though for most reproductive activity (mature egg number) declines markedly in the late dry season. Two of these (Hypocysta irius, H.metirius) are restricted to less seasonal and more favourable (wetter) areas but the three others (Ypthima arctous, H.adiante, H.pseudirius) occur widely in the relatively dry savanna, where they may specialize on grass in moister microenvironments. Second, two species (M.terminus, M.sirius) live in predictably moist habitats which are buffered from climatic extremes; they breed for much of the season but reproductive activity declines as the dry season progresses and may cease late in the season. Third, one species (M.perseus) is more opportunistic, breeding for only a limited interval during the favourable (wet) periods; during the long dry season adults contract to moist refugia and remain in reproductive diapause.
• 4 Spending the late dry season as an adult, either in diapause or with mature eggs, may improve the capacity to utilize new growth of grasses at the start of the favourable season, thereby enhancing population growth during good times. It may also provide additional flexibility to counter the temporal uncertainty of the dry season.
• 5 The strategy of residing in more equitable habitats or specializing on predictable foods may be the most restrictive in terms of distribution.

     

Developmental plasticity and acclimation both contribute to adaptive responses to alternating seasons of plenty and of stress in <Emphasis Type="Italic">Bicyclus</Emphasis> butterflies

Plasticity is a crucial component of the life cycle of invertebrates that live as active adults throughout wet and dry seasons in the tropics. Such plasticity is seen in the numerous species of Bicyclus butterflies in Africa which exhibit seasonal polyphenism with sequential generations of adults with one or other of two alternative phenotypes. These differ not only in wing pattern but in many other traits. This divergence across a broad complex of traits is associated with survival and reproduction either in a wet season that is favourable in terms of resources, or mainly in a dry season that is more stressful. This phenomenon has led us to examine the bases of the developmental plasticity in a model species, B. anynana, and also the evolution of key adult life history traits, including starvation resistance and longevity. We now understand something about the processes that generate variation in the phenotype, and also about the ecological context of responses to environmental stress. The responses clearly involve a mix of developmental plasticity as cued by different environments in pre-adult development, and the acclimation of life history traits in adults to their prevailing environment.     

Seasonal polyphenism in the wild: survey of wing patterns in five species of Bicyclus butterflies in Malawi

Abstract.

• 1 For three successive years Bicyclus butterflies were caught on a daily basis at a field site in Malawi.
• 2 Over 5000 butterflies, belonging to five species, were captured. Eight characters describing their plastic wing pattern were measured and analyzed.
• 3 Broadly speaking, the plasticity is similar for all species, with the wet season forms having conspicuous wing markings (e.g. eyespots), and dry season forms lacking these markings.
• 4 However, at a more detailed level, each species has its own specific form of plasticity with especially clear differences in the number of intermediate forms.
• 5 Females generally show a higher degree of plasticity than males.
• 6 The relative frequencies of intermediate forms and the difference between the sexes are associated with differences between the species in their preference for more open habitats or forests.
• 7 The species with the most divergent plasticity is also ecologically and phylogenetically comparatively distant from the others.

     

Matching field and laboratory environments: effects of neglecting daily temperature variation on insect reaction norms

The tropical butterfly, Bicyclus anynana, exhibits seasonal polyphenism. The wet season form has large eyespots and a pale band while these characters are much less conspicuous or absent in the dry season form. This plasticity is induced in the laboratory by use of a standard series of constant temperatures in the larval stage yielding a continuous norm of reaction. Butterflies in this study were reared from hatchling larvae in seven regimes which differed with respect to thermoperiod or photoperiod. The effect of rearing treatment on the phenotypic plasticity of the adult wing pattern, on life history traits and on larval feeding rhythms was investigated. Photoperiod had little effect except that constant light produced a higher mortality and tended to produce a longer development time. Thermoperiod had a major effect on the life history traits in comparison to a constant temperature regime with the same daily mean: development time was shorter with higher growth rates. The faster development was associated with a substantial shift in the wing pattern towards the wet season form. Larvae feed mostly at night both under constant and thermoperiod (cool nights) conditions. The results are discussed with respect to the necessity of matching field and laboratory environments in studies of norms of reaction or of life history traits where the adaptive significance of the variation is important. Fluctuating conditions in nature, especially with respect to thermoperiod, must be taken into account.     

Effects of plant structure on butterfly diversity in Mt. Marsabit Forest – northern Kenya

Butterflies, like most forest dependent animals are good ecological indicators of the health of the forests they dwell. For example, butterfly species richness decreases after a forest disturbance and fragmentation but a few species may subsequently invade the forest fragment and boost the species richness. Studies were conducted to determine the effects of human activity and seasonal changes on butterfly species in the affected new habitats. Results showed that both seasonal and habitat changes significantly affect the butterfly abundance (P = 0.0001). Similarly, there was significant correlation between plant diversity and butterfly diversity in wet season (r = 0.854) and dry season (r = 0.855). The significance of these studies as a useful tool for sustainable forest use and conservation is discussed.     

Nectar sugar and amino acid preferences of Battus philenor (Lepidoptera, Papilionidae)

Abstract.

• 1 Butterflies of Battus philenor were tested for their preferences for nectar sugars and amino acids in an outdoor cage experiment.
• 2 The butterflies clearly preferred both sucrose and fructose over glucose. They also preferred sucrose over fructose.
• 3 No other preferences were found to be statistically significant, although male butterflies tended to prefer a plain sugar solution over a sugar solution containing a mixture of amino acids: females consumed both of these solutions in almost equal proportions.
• 4 The results are discussed with respect to nectar composition of butterfly pollinated flowers, flower preferences, physiological and reproductive aspects of butterflies.

     

The occurrence and effect of a protozoan parasite, Ophryocystis elektroscirrha (Neogregarinida: Ophryocystidae) on overwintering monarch butterflies, Danaus plexippus (Lepidoptera: Danaidae) from two California winter sites

Abstract.

• 1 Monarch butterflies, Danaus plexippus, from two overwintering populations, were found to have Ophryocystis elektroscirrha spores on their scales at rates between 53% and 68%. The frequency of butterflies with O.elektroscirrha spores remained about the same between sites and throughout the winter.
• 2 The spores, recovered from all parts of the body of the butterfly, were most numerous on the abdomen, particularly near the posterior third.
• 3 Butterflies with spores survived as long as those without detectable spores at 10.1°C ±0.4 SE and 78.3% r.h. ±0.6SE. Insects with spores held at 19.4°C ±0.4SE and 44.9% r.h. ±1.5SE showed a significantly higher rate of moisture loss and survived a shorter period than monarch butterflies without detectable spores.

     

Quantitative genetic analysis of responses to larval food limitation in a polyphenic butterfly indicates environment‐ and trait‐specific effects

Different components of heritability, including genetic variance (V_G), are influenced by environmental conditions. Here, we assessed phenotypic responses of life‐history traits to two different developmental conditions, temperature and food limitation. The former represents an environment that defines seasonal polyphenism in our study organism, the tropical butterfly Bicyclus anynana, whereas the latter represents a more unpredictable environment. We quantified heritabilities using restricted maximum likelihood (REML) procedures within an “Information Theoretical” framework in a full‐sib design. Whereas development time, pupal mass, and resting metabolic rate showed no genotype‐by‐environment interaction for genetic variation, for thorax ratio and fat percentage the heritability increased under the cool temperature, dry season environment. Additionally, for fat percentage heritability estimates increased under food limitation. Hence, the traits most intimately related to polyphenism in B. anynana show the most environmental‐specific heritabilities as well as some indication of cross‐environmental genetic correlations. This may reflect a footprint of natural selection and our future research is aimed to uncover the genes and processes involved in this through studying season and condition‐dependent gene expression.     

Seasonal influence on reproduction in chimpanzees of gombe national park

Although wild chimpanzees are not seasonal breeders, there are seasonal effects on several aspects of chimpanzee reproduction. I examined the seasonal incidence of anogenital swelling in cyclic, pregnant, and acyclic female chimpanzees in Gombe National Park, May 1975–April 1992, and surveyed important reproductive events to determine whether there is a seasonal effect. I analyzed data by season (wet vs. dry) and seasonal quarter;early dry season = May–July;late dry = August–October;early wet = November–January;late wet = February–April. When data for the 17 years are combined, the percentage of females in each reproductive state remains consistent throughout the year. In a given month, 30–35% of subjects were in the cyclic category, 11–15% were pregnant, and 54–61% were acyclic. Cyclic females showed full swelling more often during the late dry season. Pregnant females exhibited anogenital swelling more often during the late dry and early wet seasons. Acyclic females also exhibited a seasonal effect with more anogenital swelling during the late dry season. There is no seasonal difference in frequency of live births (dry, 20;wet, 23). However, the timing of conception showed a seasonal effect (dry, 32;wet, 16). Consistent with earlier reports, the onset of postpartum cycles is highly seasonal;30 occurred during dry season, 9 during wet season. The occurrence of first full swellings for young females is also concentrated in the late dry season. It appears that the dry season is a time of great change for Gombe chimpanzee reproductive physiology. Previous studies indicated that seasonal changes in food availability play a role in increasing group size during the dry season and social contact between females can enhance cyclicity. Accordingly, I suggest that seasonal changes in diet may play a role, either directly (food content) or indirectly (social contact), to alter reproductive physiology.     

High within-stream replication is needed to predict litter fluxes in wet–dry tropical streams

1. Streams draining forested landscapes are fuelled by terrestrial plant litter, which can be transported downstream or retained and broken down locally. However, fluxes of plant litter in streams can vary at multiple spatio-temporal scales, affecting the availability of this key resource in heterotrophic stream food webs.
2. To explore this question we quantified several processes related to litter dynamics (i.e. litter inputs, storage, losses by transport and losses by breakdown) by sampling litter at multiple sites in three streams of the Brazilian Cerrado biome (which has a tropical wet–dry climate) for 2 years. We assessed the relative contribution of different spatial (among and within streams) and temporal scales (annual, seasonal and monthly) to total variability of these processes (hereafter fluxes).
3. Spatial and temporal variability of fluxes were both high, but spatial variation was 1.67-fold greater than temporal variation (61 versus 37%, respectively), especially at the within-stream scale (50% overall); an exception was litterfall, which varied less spatially than temporally (24 versus 76%). Temporal variation of litter storage (and hence availability to consumers) was mostly seasonal and due to differences in net transport.
4. Inputs and transport were higher in the wet than the dry season (wet versus dry season, 1.45 versus 0.92 and 1.43 versus 0.06 g litter m⁻² day⁻¹), while breakdown was similar between both seasons (0.88 versus 0.94 g litter m⁻² day⁻¹). Storage (i.e. accumulation) rate was positive and negative in the dry and wet season, respectively, indicating that litter was stored in the dry season and exported in the wet season. The transitional dry–wet season showed the highest inputs, breakdown and storage (3.21, 1.63 g litter m⁻² day⁻¹ and 145 g litter m⁻²), while the wet–dry season showed lower inputs (as in the dry season), higher transport (as in the wet season) and lower breakdown and storage than the other seasons (0.93, 0.65, 0.31 g litter m⁻² day⁻¹ and 24 g litter m⁻²).
5. Our results underscore the role of variation in biophysical drivers of litter fluxes within streams (e.g. pool–riffle configuration, substrate features, biological communities), and suggest that high within-stream replication is necessary to study litter fluxes at larger scales and over time. The seasonal patterns suggested potential changes in litter dynamics under future climate scenarios in the tropics, including increased storage due to reduced transport in a drier climate.

     

The conceptual and practical implications of interpreting diet breadth mechanistically in generalist predatory insects

Seasonal polyphenism in animal colour patterns indicates that temporal variation in selection pressures maintains phenotypic plasticity. Spring generation of the polyphenic European map butterfly Araschnia levana has an orange–black fritillary‐like pattern whilst individuals of the summer generation are black with white bands across the wings. What selects for the colour difference is unknown. Because predation is a major selection pressure for insect coloration, we first tested whether map butterfly coloration could have a warning function (i.e. whether the butterflies are unpalatable to birds). In a following field experiment with butterfly dummies we tested whether the spring form is better protected than the summer form from predators in the spring, and vice versa in the summer. The butterflies were palatable to birds (blue tits Cyanistes caeruleus) and in the field the spring and summer form dummies were attacked equally irrespective of season. Therefore, we found no evidence that the map butterfly is warning‐coloured or that seasonal polyphenism is an adaptation to avian predation. Because insect coloration has multiple functions and map butterfly coloration is linked to morphology, life history and development it is likely that the interplay of several selection pressures explains the evolution of colour polyphenism. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Phenotypic plasticity of starvation resistance in the butterfly <Emphasis Type="Italic">Bicyclus anynana</Emphasis>

Starvation resistance is an important trait related to survival in many species and often involves dramatic changes in physiology and homeostasis. The tropical African butterfly Bicyclus anynana lives in two seasonal environments and has evolved phenotypic plasticity. The contrasting demands of the favourable, wet season and the harsh, dry season have shaped a remarkable life history, which makes this species particularly interesting for investigating the relationship between starvation resistance, metabolism, and its environmental modulation. This study reports on two laboratory experiments to investigate the effects of pre-adult and adult temperatures that mimic the seasonal environments, on starvation resistance and resting metabolic rate (RMR) in adult B. anynana. In addition, we investigate starvation resistance in wet and dry seasonal form genotypes; artificial selection on eyespot size has yielded lines that only produce one or the other of the seasonal forms across all rearing environments. As expected, the results show a large effect of adult temperature. More relevant, we show here that both pre-adult temperature and genetic background also influence adult starvation resistance, showing that phenotypic plasticity in this species includes starvation resistance. The dry season form genotype has a higher starvation resistance when developed at dry season temperatures, indicating a genetic modulation of starvation resistance in relation to temperature. Paradoxically, dry season pre-adult temperatures reduce starvation resistance and raise RMR. The high overall association of RMR and starvation resistance in our experiments suggests that energy expenditure and survival are linked, but that they may counteract each other in their influence on fitness in the dry season. We hypothesize that metabolism is moderating a trade-off between pre-adult (larval) survival and adult survival in the dry season.     

Spatial and temporal variation of fish community biomass and energy flow throughout a tropical river network

1. Accurately accounting for flows of energy through food webs is challenging because of the spatial and temporal variability associated with energy production and consumption. Wet–dry tropical rivers have a highly seasonal discharge regime where wet season flows allow access to energy sources (inundated wetlands) that are not available during the dry season when aquatic consumers are confined to disconnected waterholes.
2. We combined measures of fish community biomass with previously published feeding guild specific stable isotope analyses to explore how opposing wet- and dry-season habitat templates influence spatial and temporal trends in the sources of energy supporting fish biomass throughout a river network in the wet–dry tropics of northern Australia.
3. Accounting for the relative contribution of each feeding guild to fish community biomass was a critical component of our analyses, as a single feeding guild (invertivore/piscivore) influenced spatial and temporal patterns in the sources of energy supporting overall fish biomass. During the early dry season, the reliance of fish communities on autochthonous sources of energy (periphyton) decreased from the upper to lower reaches of the river network, which correlates with increasing floodplain area and wet season inundation times. These patterns disappeared by the late dry season as fish in both upper and lower reaches became increasingly reliant on autochthonous sources produced within waterholes over the course of the dry season, indicating that the large wet-season gains in fish biomass are maintained through the dry season by energy produced within waterhole refuges.
4. Collectively these results indicate that a combination of autochthonous and allochthonous sources of energy work in unison to support fish community biomass throughout the Mitchell River catchment and that access to these sources of energy is dictated by seasonal patterns in discharge interacting with spatial variability in river geomorphology (channel geometry and floodplain area).
5. Many rivers are experiencing decreased flows due to water resource development and more frequent and severe droughts. Thus, we suggest our study provides insight into how changes in discharge regime could influence food web energetics throughout river networks.

     

Eyespots deflect predator attack increasing fitness and promoting the evolution of phenotypic plasticity

Some eyespots are thought to deflect attack away from the vulnerable body, yet there is limited empirical evidence for this function and its adaptive advantage. Here, we demonstrate the conspicuous ventral hindwing eyespots found on Bicyclus anynana butterflies protect against invertebrate predators, specifically praying mantids. Wet season (WS) butterflies with larger, brighter eyespots were easier for mantids to detect, but more difficult to capture compared to dry season (DS) butterflies with small, dull eyespots. Mantids attacked the wing eyespots of WS butterflies more frequently resulting in greater butterfly survival and reproductive success. With a reciprocal eyespot transplant, we demonstrated the fitness benefits of eyespots were independent of butterfly behaviour. Regardless of whether the butterfly was WS or DS, large marginal eyespots pasted on the hindwings increased butterfly survival and successful oviposition during predation encounters. In previous studies, DS B. anynana experienced delayed detection by vertebrate predators, but both forms suffered low survival once detected. Our results suggest predator abundance, identity and phenology may all be important selective forces for B. anynana. Thus, reciprocal selection between invertebrate and vertebrate predators across seasons may contribute to the evolution of the B. anynana polyphenism.     

Phenotypic plasticity in field populations of the tropical butterfly Hypolimnas bolina (L.) (Nymphalidae)

Phenotypic plasticity may enable organisms to maximize their fitness in seasonally variable environments. However, in butterflies, seasonal polyphenism is often striking but functionally obscure. This paper addresses the possible adaptive significance of phenotypic variation in the tropical butterfly Hypolimnas bolina (L.) (Nymphalidae). Plasticity in body size and wing coloration can be elicited in this species under laboratory conditions, however it is not known how this plasticity is expressed in the wild. Moreover, adult H. bolina spend the winter dry season in a reproductive diapause, which allows certain predictions regarding the occurrence of seasonal plasticity. Based on consideration of the requirements of diapausing and directly developing individuals, we predicted that if seasonal plasticity in phenotype were adaptive, then overwintering individuals should be larger and darker than their directly developing counterparts. This prediction was largely - although not entirely - fulfilled. Dry season butterflies were duller and darker than their wet season counterparts (this plasticity was superimposed on a genetic colour polymorphism), however size plasticity varied geographically. Dry season adults were consistently larger than wet season adults in the tropical north, but not in the south. We use these findings to discuss the possible adaptive significance of seasonal variation in the colour and size of this tropical butterfly.     

Diaspore dispersal season influences root growth and seed traits,but not germination responses,of sympatric Piper species in a seasonal forest

• Seeds may differ in terms of dormancy, longevity, sensitivity to desiccation and dry mass, according to the timing (dry season/rainy season) of diaspore dispersal. In addition, seasonal variations in temperature and water availability can act as signals of the season during seed development, influencing germination responses and root growth. We evaluated the effects of temperature variations and water availability on germination parameters, root growth and seed traits of four coexisting Piper species in seasonal vegetation that differed in diaspore dispersal timing.
• Eight temperature treatments (15, 20, 23, 25, 28, 30, 35 °C, and alternate 30 °C–20 °C) and four induced water potentials (0, −0.3, −0.6 and −1.2 MPa) were used. The parameters germination onset, germination percentage (G%), mean germination time (MGT), root elongation, seed longevity during ex situ storage and dry mass of seeds were evaluated.
• Germination responses observed were independent of the diaspore dispersal timing, such as variations in germination onset, G% and MGT, both in temperature and water availability treatments. In contrast, root elongation, longevity and dry mass of seeds varied according to the time of diaspore dispersal.
• Our results corroborate the hypothesis that the timing of diaspore dispersal is an important factor in controlling the initial development of seedlings in seasonal vegetation, but not in germination responses. The predominance of negative effects of temperature increases and water deficit on root growth shows that the initial stages of plant development can be strongly impacted by these environmental factors.

     

Divergent response of seasonally dry tropical vegetation to climatic variations in dry and wet seasons

Interannual variations of photosynthesis in tropical seasonally dry vegetation are one of the dominant drivers to interannual variations of atmospheric CO₂ growth rate. Yet, the seasonal differences in the response of photosynthesis to climate variations in these ecosystems remain poorly understood. Here using Normalized Difference Vegetation Index (NDVI), we explored the response of photosynthesis of seasonally dry tropical vegetation to climatic variations in the dry and the wet seasons during the past three decades. We found significant (p < 0.01) differences between dry and wet seasons in the interannual response of photosynthesis to temperature (γ^int) and to precipitation (δ^int). γ^int is ~1% °C^?1 more negative and δ^int is ~8% 100 mm^?1 more positive in the dry season than in the wet season. Further analyses show that the seasonal difference in γ^int can be explained by background moisture and temperature conditions. Positive γ^int occurred in wet season where mean temperature is lower than 27°C and precipitation is at least 60 mm larger than potential evapotranspiration. Two widely used Gross Primary Productivity (GPP) estimates (empirical modeling by machine‐learning algorithm applied to flux tower measurements, and nine process‐based carbon cycle models) were examined for the GPP–climate relationship over wet and dry seasons. The GPP derived from empirical modeling can partly reproduce the divergence of γ^int, while most process models cannot. The overestimate by process models on negative impacts by warmer temperature during the wet season highlights the shortcomings of current carbon cycle models in representing interactive impacts of temperature and moisture on photosynthesis. Improving representations on soil water uptake, leaf temperature, nitrogen cycling, and soil moisture may help improve modeling skills in reproducing seasonal differences of photosynthesis–climate relationship and thus the projection for impacts of climate change on tropical carbon cycle.     

Seasonality of reproduction in Asian elephants Elephas maximus and African elephants Loxodonta africana: underlying photoperiodic cueing?

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