Variación en el tamaño de los huevos en garzas (Aves: Ardeidae) que anidan en la ciénaga de Birama, Cuba / Egg size variation in egrets and herons (Aves: Ardeidae) nesting in Birama’s swamp, Cuba

Intraclutch egg size variation in birds depends on many ecological factors and on the evolutive history of each species. In wading birds, a trend to smaller eggs with laying order has been described, but comparative reports are scarce. In this study, egg size variation patterns were described for nine Egrets and Heron species nesting in Birama’ Swamp, Cuba. The patterns were described using external dimensions of 3 142 eggs from 1 875 nests of Butorides virescens, Bubulcus ibis, Ardea alba, Nycticorax nycticorax, Nyctanassa violacea and four Egretta species, taken in the field between 1998 and 2006. Results showed that eggs were 4.9-10% of adult weight and had volume variation coefficients between 6-9%. There were no general and consistent interspecies relationship between clutch size and egg sizes. Average volumes tend to get smaller with laying order, but it is not statistically detectable in Butorides and Bubulcus. Last egg was between 0.2% and 15% smaller than the first, showing an inverse relationship with it. Intraclutch asymmetry is light in E. thula and fluctuating around null in Bubulcus. Size only predicted laying or hatching order for the last egg, in nests with more than two eggs, with 72.4% of confidence.

Las variaciones intranidada de la talla de los huevos de las aves responden a numerosos factores ecológicos y de la historia evolutiva de las especies. En las zancudas aunque se ha descrito una disminución de la talla con el orden de puesta, los trabajos comparativos entre especies son escasos. En este trabajo se describen los patrones de variación del tamaño de los huevos de nueve especies de garzas (Aves: Ardeidae) nidificantes en la ciénaga de Birama, Cuba. Los patrones se describen a partir de las dimensiones de 3 142 huevos, pertenecientes a 1 875 nidos de Butorides virescens, Bubulcus ibis, Ardea alba, Nycticorax nycticorax, Nyctanassa violacea y cuatro especies de Egretta, tomados en la ciénaga de Birama, Cuba, entre 1998 y 2006. Los huevos representaron entre el 4.9-10% del peso adulto y tuvieron un coeficiente de variación del volumen entre el 6-9%. No existió una relación general consistente entre especies entre el tamaño de puesta y las dimensiones de los huevos. El volumen promedio del huevo tiende a disminuir con el orden de puesta, pero no es estadísticamente detectable en Butorides y Bubulcus. El último huevo fue entre un 0.2 y un 15% menor que el primero, disminuyendo su volumen relativo con la talla del primer huevo. La asimetría intranidada es menos marcada en E. thula y prácticamente fluctuante alrededor de cero en Bubulcus. En general, la talla del huevo solo puede predecir el orden de puesta para el último huevo en nidadas mayores de dos con un 72.4% de confianza.

Patterns of investment of the reproductive strategy of two stream-dwelling Characidae

The reproductive strategy of two congeneric species (Astyanax janeiroensis - AJ and Astyanax hastatus - AH) was assessed, in order to address the costs imposed by different investment patterns, on four major life history characters: migratory behaviour, breeding time, fecundity and egg size. Altitudinal segregation of young and adult individuals plus data from the literature indicated that AJ is a migratory species, whereas AH is non migratory. Breeding season (BS) analysis revealed that AH was reproductively active year-round (12 months), whereas AJ breeds during 9 months. Brood costs (Ovarian Investment) were almost the same for both species (AJ - 364 oocytes / g and egg volume = 0.52 mm³; AH -702 oocytes / g and egg volume = 0.27 mm³). Reproductive costs (RC), considered as product of gamete production (OI) and gamete output (BS), were 1,703.7 for AJ and 2,274.0 for AH; thus RC is 25 percent higher in AH. It is concluded that the costs with OI (egg size and egg numbers) are equal for both species but as breeding season is larger for AH the overall strategy is 25 percent more expensive in AH. Thus, it is hypothesized that this 25 percent should be considered as the extra costs that AJ uses during migration and is compensated by its shorter breeding time (9 months versus 12 months of AH).

A estratégia reprodutiva de duas espécies congenéricas (Astyanax janeiroensis - AJ e Astyanax hastatus - AH) foi analisada a fim de se determinar os custos energéticos impostos por diferentes padrões de investimento em quatro dos principais caracteres da história de vida de peixes: comportamento migratório, estação reprodutiva, fecundidade e tamanho dos ovócitos. A segregação espacial dos indivíduos jovens e adultos associada a informações da literatura indicaram que AJ é uma espécie migratória enquanto AH não migra. A análise sobre a estação reprodutiva (ER) revelou que AH se reproduz ao longo de todo o ciclo anual (12 meses) enquanto AJ se reproduz durante 9 meses. Os custos com a desova (Investimento Ovariano - IO) foram similares nas duas espécies (AJ - 364 ovócitos/g e volume dos ovócitos = 0,52 mm³; AH - 702 ovócitos/g e volume dos ovócitos = 0,27 mm³). O custo da reprodução (CR), considerado como o produto da produção de gametas (IO) e o tempo de liberação dos gametas (ER), foram 1.703,7 para AJ e 2.274,0 para AH; assim CR é 25 por cento superior em AH. Concluímos assim, que os custos com IO (tamanho e número de ovócitos) são iguais para as duas espécies, mas como a estação reprodutiva é maior para AH, a estratégia como um todo é mais custosa para AH. Dessa forma, sugerimos que os 25 por cento excedentes podem ser considerados como os custos extras que AJ necessita para a migração e são compensados pelo menor tempo da estação reprodutiva (9 meses em AJ versus 12 meses em AH).

Tamaño corporal, tolerancia ecológica y potencial de bioindicación de la calidad del agua de Anacroneuria spp. (Plecoptera: Perlidae) en América del Sur / Body size, ecological tolerance and potential for water quality bioindication in the genus Anacroneuria (Plecoptera: Perlidae) from South America

Knowledge about the biology and ecology of neotropical aquatic taxa is crucial to establish general ecological rules and water protection systems. Based mainly on published data, the present work shows the following biological and ecological characteristics of Anacroneuria species (Klapálek 1909): (a) the wide range of environmental conditions of rivers where Anacroneuria species occur, (b) species number decreases along an increasing elevation gradient, (c) body size increases in relation to the maximum altitude of occurrence, (d) altitudinal range increases with body size, (e) there is a constant relationship between male and female body size, and finally, (f) larger females lay larger eggs. In temperate countries, the family Perlidae in general, and the genus Anacroneuria in particular, are viewed as excellent water quality indicators. We suggest that, considering the complexity of the group's ecology in South America, it should not be automatically considered an excellent bioindicator in the Neotropical region.