Seasonal polyphenism in Bicyclus dorothea (Lepidoptera: Nymphalidae) across different habitats in Cameroon

Open Access Article; Published online: 14 Sept 2018Many organisms exhibit changes in phenotypic traits as a response to seasonal environmental variation. We investigated the role of habitat in generating seasonal polyphenism in different populations of the light bush brown butterfly Bicyclus dorothea (Cramer, 1779) (Lepidoptera: Nymphalidae) in Cameroon. Butterflies were caught during the wet and dry seasons across four localities representing two distinct habitats, namely forest and ecotone (forest–savanna transition zone) over a 2-yr period (2015–2016). We found distinct variation in the wing pattern characteristics of butterflies in response to seasonality and habitat. Specifically we observed that: 1) all wing characters are not seasonally plastic in B. dorothea; 2) populations from ecotone tend to be more variable, with individuals exhibiting wings with large spots during the wet season and very reduced spots in the dry season while in forest populations, individuals exhibit wings with large spots during the wet season, but in the dry season, spots are not as greatly reduced as their ecotone counterparts; 3) this polyphenism in B. dorothea alternated consistently during the wet and dry seasons over the 2 yr of sampling. Bicyclus species have become a textbook example of seasonal polyphenism while this study extends this model system to the unique forest–ecotone gradient of Central Africa and demonstrates the complexity of seasonal forms in different habitats

Local adaptation in thermal tolerance for a tropical butterfly across ecotone and rainforest habitats

Open Access Journal; Published online: 01 Apr 2021Thermal adaptation to habitat variability can determine species vulnerability to environmental change. For example, physiological tolerance to naturally low thermal variation in tropical forests species may alter their vulnerability to climate change impacts, compared with open habitat species. However, the extent to which habitat-specific differences in tolerance derive from within-generation versus across-generation ecological or evolutionary processes are not well characterized. Here we studied thermal tolerance limits of a Central African butterfly (Bicyclus dorothea) across two habitats in Cameroon: a thermally stable tropical forest and the more variable ecotone between rainforest and savanna. Second generation individuals originating from the ecotone, reared under conditions common to both populations, exhibited higher upper thermal limits (CTmax) than individuals originating from forest (∼3°C greater). Lower thermal limits (CTmin) were also slightly lower for the ecotone populations (∼1°C). Our results are suggestive of local adaptation driving habitat-specific differences in thermal tolerance (especially CTmax) that hold across generations. Such habitat-specific thermal limits may be widespread for tropical ectotherms and could affect species vulnerability to environmental change. However, microclimate and within-generation developmental processes (e.g. plasticity) will mediate these differences, and determining the fitness consequences of thermal variation for ecotone and rainforest species will require continued study of both within-generation and across-generation eco-evolutionary processes

Geographic distribution and abundance of the Afrotropical subterranean scale insect Stictococcus vayssierei (Hemiptera: Stictococcidae), a pest of root and tuber crops in the Congo basin

Open Access Article; Published online: 01 Oct 2019Stictococcus vayssierei is a major pest of root and tuber crops in central Africa. However, data on its ecology are lacking. Here we provide an updated estimate of its distribution with the aim of facilitating the sustainable control of its populations. Surveys conducted in nine countries encompassing 13 ecological regions around the Congo basin showed that African root and tuber scale was present in Cameroon, Central African Republic, Congo, Democratic Republic of Congo, Equatorial Guinea, Gabon and Uganda. It was not found on the sites surveyed in Chad and Nigeria. The pest occurred in the forest and the forest-savannah mosaic as well as in the savannah where it was never recorded before. However, prevalence was higher in the forest (43.1%) where cassava was the most infested crop, compared to the savannah (9.2%) where aroids (cocoyam and taro) were the most infested crops. In the forest habitat, the pest was prevalent in all but two ecological regions: the Congolian swamp forests and the Southern Congolian forest-savanna mosaic. In the savannah habitat, it was restricted to the moist savannah highlands and absent from dry savannahs. The scale was not observed below 277 m asl. Where present, the scale was frequently (87.1% of the sites) attended by the ant Anoplolepis tenella. High densities (>1000 scales per plant) were recorded along the Cameroon–Gabon border. Good regulatory measures within and between countries are required to control the exchange of plant materials and limit its spread. The study provides information for niche modeling and risk mapping

DFT study of pressure induced phase transitions in LiYF4

An investigation of the pressure induced phase transition from the scheelite phase (I41/a, Z=4) to the fergusonite-like phase (I2/a, Z=4)/LaTaO(P21/c, Z=4) of LiYF4 is presented. Employing density functional theory (DFT) within the generalized gradient approximation, the internal degrees of freedom were relaxed for a pressure range of 0 GPa to 20 Gpa. The influence of pressure on the lattice vibration spectrum of the scheelite phase (I41/a, Z=4) was evaluated using the direct approach, i.e. using force constants calculated from atomic displacements. The transition volume is in good agreement with experiment, while the transition pressure is overestimated of 6 GPa. At 20 GPa, a P21/c structure with apentacoordinated lithium cation is found to be the most stable phase. This structure is compatible with a transition driven by a Bg zone-center soft optic mode linked to a soft-acoustic mode along the [11-1] direction as observed for the proper ferroelastic transition of BiVO4

Structure et dynamique des infracommunautés de Myxosporidies parasites de Ctenopoma petherici GÜNTHER, 1864 (Anabantidae), Clarias pachynema BOULENGER, 1903 (Clariidae) et Hepsetus odoe (BLOCH, 1794) (Hepsetidae) dans la rivière Sangé au Cameroun

L’examen de Ctenopoma petherici, Clarias pachynema et Hepsetus odoe récoltés dans la rivière Sangé au Cameroun entre janvier 2008 et mars 2009 a révélé la présence de 11 espèces de Myxosporidies. Parmi les espèces parasites identifiées, Myxobolus pethericii et Henneguya pethericii sont apparues fréquentes (Pr > 50%); Myxobolus sp.1, Myxobolus sp.2, Myxobolus gariepinus, Myxobolus africanus, Henneguya nkamensis, Myxidium petrocephali et Myxidium nkamensis sont apparues secondaires (10% £ Pr £ 50%), tandis que Myxobolus camerounensis et Myxidium sangei sont apparues rares (Pr < 10%). La charge kystique moyenne est apparue élevée (x̄ > 100 kystes) pour H. pethericii et H. nkamensis; moyenne (50 kystes < x̄ £ 100 kystes) pour Myxobolus sp.1, Myxobolus sp.2, M. pethericii, M. africanus, et très faible (x̄ < 10 kystes) pour M. gariepinus. Le pourcentage d’infestation décroît lorsque la taille du poisson augmente pour les espèces parasites suivantes : M. pethericii, M. gariepinus, H. pethericii, H. nkamensis et M. nkamensis. Par ailleurs, la charge kystique moyenne diminue lorsque la taille de l’hôte augmente pour M. pethericii et H. pethericii. Hormis le fait que les individus femelles sont fréquemment plus parasités par H. pethericii que les mâles, le sexe de l'hôte n'a pas d'influence sur le parasitisme des Myxosporidies étudiées. La saison sèche s’est avérée favorable à l’occurrence de Myxobolus sp.2 alors que M. petrocephali, M. nkamensis et M. gariepinus ont été plus fréquentes en saison de pluies. La charge kystique moyenne de H. pethericii et M. pethericii est plus importante en saison sèche.Mots clés : Prévalence, charge kystique, poisson, eaux douce

Henneguya mbakaouensis sp. nov., Myxobolus nounensis sp. nov. and M. hydrocyni Kostoingue & Toguebaye, 1994, Myxosporea (Myxozoa) parasites of centropomidae, Cichlidae and Characidae (Teleosts) of the Sanaga basin in Cameroon (Central Africa)

The study of 102 teleost freshwater fishes of Sanaga basin in Cameroon revealed the presence of three myxosporean species, among which two were new. Host fishes were of three families: Centropomidae, Cichlidae and Characidae. New species were identified as Henneguya mbakaouensis sp. nov., a gill parasite of Lates niloticus and Myxobolus nounensis sp. nov. found in the kidney and spleen of Sarotherodon galilaeus and Tilapia mariae. Myxobolus hydrocyni Kostoïngue & Toguebaye, 1994, previously described in Chad, was also found in Cameroon; complementary informations were given on that parasite which seemed to be specific to its host

sp. nov.,

The study of 102 teleost freshwater fishes of Sanaga basin in Cameroon revealed the presence of three myxosporean species, among which two were new. Host fishes were of three families: Centropomidae, Cichlidae and Characidae. New species were identified as Henneguya mbakaouensis sp. nov., a gill parasite of Lates niloticus and Myxobolus nounensis sp. nov. found in the kidney and spleen of Sarotherodon galilaeus and Tilapia mariae. Myxobolus hydrocyni Kostoïngue & Toguebaye, 1994, previously described in Chad, was also found in Cameroon; complementary informations were given on that parasite which seemed to be specific to its host

Deux espèces nouvelles de

L’examen de Clarias pachynema Boulenger, 1903 (Clariidae), Ctenopoma petherici Günther, 1864 (Anabantidae) et Parachanna obscura (Günther, 1861) (Channidae), capturés dans le bassin du Nkam au Cameroun, a révélé la présence de deux espèces nouvelles de Myxosporidies du genre Myxidium Bütschli, 1882, toutes parasites de la vésicule biliaire. Les espèces inédites sont : Myxidium nkamensis n. sp., parasite de Clarias pachynema; M. sangei n. sp., qui forme des spores dans la paroi de la vésicule biliaire de Parachanna obscura. Deux autres espèces, Myxidium petrocephali Fomena et Bouix, 1986 et M. distichodi Kostoïngué, Faye et Toguebaye, 1998, ont été retrouvées chez des hôtes nouveaux. Leur diagnose est complétée. La liste des espèces de Myxidium parasites des poissons d’eau douce d’Afrique est donnée

Deux espèces nouvelles de Myxidium (Myxosporea : Myxidiidae) parasites de poissons d’eau douce du Cameroun

L’examen de Clarias pachynema Boulenger, 1903 (Clariidae), Ctenopoma petherici Günther, 1864 (Anabantidae) et Parachanna obscura (Günther, 1861) (Channidae), capturés dans le bassin du Nkam au Cameroun, a révélé la présence de deux espèces nouvelles de Myxosporidies du genre Myxidium Bütschli, 1882, toutes parasites de la vésicule biliaire. Les espèces inédites sont : Myxidium nkamensis n. sp., parasite de Clarias pachynema; M. sangei n. sp., qui forme des spores dans la paroi de la vésicule biliaire de Parachanna obscura. Deux autres espèces, Myxidium petrocephali Fomena et Bouix, 1986 et M. distichodi Kostoïngué, Faye et Toguebaye, 1998, ont été retrouvées chez des hôtes nouveaux. Leur diagnose est complétée. La liste des espèces de Myxidium parasites des poissons d’eau douce d’Afrique est donnée

Description de trois espèces nouvelles de Myxosporidies (Myxozoa : Myxosporea) parasites de

L'examen de Citharinus citharus (Geoffroy Saint-Hilaire, 1809 (Teléostéen, Citharinidae), récolté sur le fleuve Chari au Tchad, a révélé la présence de trois espèces nouvelles de Myxosporidies dont nous donnons ici la description complète : Thelohanellus taguii n. sp., parasite systémique; Myxobolus mbailaoi n. sp., parasite des opercules, de la peau et de l'intestin et Myxobolus charii n. sp., parasite de la peau