Environmental drivers on leaf phenology of ironstone outcrops species under seasonal climate

ABSTRACT Banded iron formations (BIF) have a particular vegetation type and provide a good model system for testing theories related to leaf phenology, due to unique stressful environmental conditions. As a consequence of the stressful conditions of BIF environment, we hypothesize that most species would retain at least some significant canopy cover, even at the end of the dry season, independently of growth form - trees, shrubs, and sub-shrubs. Considering the strong seasonality, we also hypothesize that photoperiod and rainfall act as triggers for leaf fall and leaf flushing in these environments. The majority of the fifteen studied species had a semi-deciduous behavior and shed their leaves mainly during the dry season, with a recovery at the end of this season. In general, leaf flushing increased around the spring equinox (end of the dry season and start of the rainy season). A trade-off between leaf loss and leaf maintenance is expected in a community in which most plants are naturally selected to be semi-deciduous. Our results suggest photoperiod as a dominant factor in predicting leaf phenology.

Histological and morphometric analysis of testes of adult quail (Coturnix coturnix japonica) of Bangladesh / Análisis histológico y morfométrico de testiculos de codorniz adulta (Coturnix coturnix japonica) de Bangladesh

A histological and morphometric study was conducted to evaluate the seasonal testicular variations in the adult Japanese quail (Coturnix coturnix japonica) in Bangladesh. The weight of birds and testes, volume, length, circumference, seminiferous tubule diameter, circumference and height of germinal epithelium of testes were measured. Sections of testes obtained from studied birds were stained with H&E and images were taken by J software. Weight and volume of paired testes of quails significantly heavier (P<0.05) in long day period of summer and rainy season (March ­ September) than the short day period of autumn and winter (October ­ February). Seasons had no significant effect on live weight gain of quails. The weight and diameter of testes or height of the germinal epithelium of the seminiferous tubule were positively correlated (r=0.84; r=0.88). Spermatogenic activity was pronounced during summer and rainy season than that of autumn and winter (P<0.05).

Se realizó un estudio histológico y morfométrico para evaluar las variaciones testiculares estacionales de la codorniz japonesa adulta (Coturnix coturnix japonica) en Bangladesh. Se midieron el peso de las aves y sus testículos; el volumen, longitud, circunferencia y diámetro de los túbulos seminíferos, y la circunferencia y altura del epitelio germinal testicular. Secciones de testículos obtenidos de las aves estudiadas fueron teñidas con H&E y las imágenes fueron analizadas con el programa ImageJ. Se registró un aumento significativo en peso y volumen de los testículos de codornices (P<0,05) en el periodo día de verano y en la temporada de lluvia (marzo-septiembre) al período del día corto de otoño e invierno (octubre-febrero). El período estacionario no tuvo efecto significativo sobre el aumento de peso vivo de las codornices. El peso y el diámetro de los testículos, y la altura del epitelio germinal del túbulo seminífero se correlacionaron positivamente (r=0,84; r=0,88). La actividad espermatogénica fue más pronunciada durante el verano y durante la temporada de lluvias que en otoño e invierno (p<0,05).

Photoperiodism and seasonality in neotropical population of Plutella xylostella L. (Lepidoptera: Yponomeutidae) / Fotoperiodismo e sazonalidade em população neotropical de Plutella xylostella L. (Lepidoptera: Yponomeutidae)

Neotropical populations of the diamondback moth Plutella xylostella L. have seasonal cycles of growth and decrease, and moth migration plays a fundamental role in generating such population dynamics. Since the oscillation of these populations is predictable, photoperiod might operate as a signal that triggers the migratory behaviour of the insect. Migration in insects is usually preceded by reproductive diapause, a photoperiodic response that can be characterised by morphological, physiological and behavioural alterations that permit to discriminate between migratory and non-migratory forms. In this study, I tested whether the pre-imaginal and reproductive development of P. xylostella from Minas Gerais (Brazil) is affected by artificial day-lengths that are equivalent to the periods of natural population growth or decrease. No evidence of photoperiodic response was found for the insect reared in laboratory on five different constant photoperiods, from 8h to 16h of light per day. There was no significant variation in survival and duration of egg, larva, and pupa stages or in pupal weight, adult size (forewing length), fecundity, and longevity. Although some species have geographically distinct photoperiodic responses, previous assumptions that cosmopolitan P. xylostella responds to photoperiod in temperate regions was questioned. Migratory and population seasonality among neotropical populations of P. xylostella certainly occurs independently of the photoperiodic announcement of seasonal changes in habitat quality.

Populações neotropicais de Plutella xylostella L. possuem ciclos sazonais de crescimento e declíneo e a migração é um fator-chave na geração da dinâmica populacional. Devido à previsibilidade sazonal das oscilações populacionais, o fotoperíodo poderia agir como o sinal que desencadea o comportamento migratório do inseto. Migrações de insetos são geralmente precedidas por diapausa reprodutiva, uma típica resposta fotoperiódica caracterizada por alterações morfológicas, fisiológicas e comportamentais que possibilitam discriminar as formas migratórias das não-migratórias. Neste estudo, foi testado se o desenvolvimento pré-imaginal e reprodutivo de P. xylostella, proveniente de Minas Gerais, é inibido por fotoperíodos equivalentes aos comprimentos de dias em que ocorrem as fases de crescimento ou de declínio das populações naturais. Nenhuma evidencia de resposta fotoperiódica foi encontrada para os insetos criados em laboratório sob cinco regimes constantes de fotoperíodos, variando de oito a dezesseis horas-luz-dia. Não houve variação significativa na sobrevivência e na duração dos estágios de ovo, larva e pupa. O peso das pupas também não foi afetado, assim como o tamanho, a fecundidade e a longevidade dos adultos. Embora algumas espécies de insetos possuam respostas fotoperiódicas geograficamente diferenciadas, a sugestão de alguns autores de que a cosmopolita P. xylostella responde ao fotoperíodo em regiões de clima temperado foi questionada. Os dados experimentais não suportaram a hipótese de que a sazonalidade migratória e populacional de P. xylostella dependem do fotoperíodo como sinal de anúncio de mudanças temporais na qualidade do habitat.

Photorefractoriness in the black-headed bunting Emberiza melanocephala: Possible involvement of the thyroid glands.

In the male black-headed bunting, Emberiza melanocephala, photostimulated testicular and/or body weight growth was followed by the regression. Transfer of photorefractory birds from 20L/4D to 23L/1D or from natural lighting (12-13 h) to 20L/4D failed to evoke testicular and/or body weight recrudescence. Thyroidectomy suppressed light-induced increase in the testes and resulted in early regression. Fully developed testes of breeding birds also regressed following thyroidectomy; an effect which was reversed by daily injections of 1 μg/bird of L-T4. Treatment with L-T4 at doses from 0·5-2·0 μg/bird/day/ 30 days had no effect on the testes of birds maintained on 12L/12D or following a shift from 12L/12D to 20L/4D. Photoinduced increase in body weight was inhibited by thyroidectomy; an effect which was reversed by treatment with L-T4 at dose level 1 μg/bird/day. The extent to which thyroidectomy decreased body weight of birds depended upon the lipid reserves at the time of operation. It is suggested that in the male black-headed bunting (i) breeding is terminated by development of absolute-gonadal and metabolic-photorefractoriness and (ii) thyroid hormones are necessary for sustaining light-induced increase in the gonads and/or body weight and for their maintenance, but not for the development of photorefractory state.