Pathology of enteric infections induced by the acanthocephalan Profilicollis chasmagnathi in Olrog's gull, Larus atlanticus, from Argentina

Acanthocephalans can be pathogenic helminths of marine birds. Every year during the breeding season, there is variable mortality among prefledged chicks from the largest known Olrog's gull (Larus atlanticus) colony. Mortality has been associated with infection by the acanthocephalan Profilicollis chasmagnathi. Our aim was to study the role of chicks' size as a risk factor for intensity of infection and severe pathology, and to expand upon previous pathological findings reported in acanthocephalan-infected chicks. Size of the chick was associated with intensity of infection and number of intestinal perforations, which increased by 6.9% and 4.1%, respectively, for each millimetre increment in chick size. Infection was associated with inflammatory enteritis and granulomatous peritonitis. Complete intestinal perforations were observed in 85% and 97.3% of the studied chicks in 2005 and 2006, respectively, and they were observed very early during the post-hatching period. Our results show: (1) the presence of advanced pathology associated with acanthocephalan infections in chicks, beginning very early in the post-hatching period; and (2) significant increases in the intensity of infection and the associated pathology as a function of size of chicks, in dead chicks during this period.

Seasonal Changes in Brood Sex Composition in Audouin's Gulls

We examined seasonal variation in the hatching sex ratio of Audouin's Gull (Larus audouinii). This species is sexually size dimorphic (males are 20% larger than females at fledging); it has a modal clutch of three eggs, which vary in size (the third egg is the smallest) and hatch asynchronously. These sex, egg size, and hatching patterns generate substantial within-brood differences in chick size that interact with the food provisioning of the parents to influence chick survival. Parental provisioning capacity depends on both parental quality and environmental conditions, both of which are known to decline with season. Consequently, the optimal brood composition is likely to vary within a season. Using molecular markers to sex newly hatched chicks, we found that offspring sex was influenced by an interaction between hatching date and hatching order, with the proportion of males among third-hatched chicks initially increasing and then decreasing later in the season.Cambios Estacionales en la Proporción de Sexos de las Polladas en Larus audouiniiResumen. En el presente trabajo examinamos la variación estacional en la proporción de sexos de los pollos de Larus audouinii en el momento de la eclosión. Esta especie es sexualmente dimórfica (los machos son un 20% mayores que las hembras al acabar su crecimiento), tiene una puesta modal de tres huevos, que varían en tamaño (el tercero es el menor) y eclosionan asincrónicamente. Estos patrones de sexo, tamaño del huevo y orden de eclosión generan diferencias sustanciales en el tamaño de los pollos dentro de la pollada, los que a su vez interaccionan con la provisión de alimento de los progenitores influyendo la supervivencia de cada pollo. La capacidad de proveer alimento dependerá de la calidad parental y de las condiciones ambientales, las cuales suelen disminuir a lo largo de la estación reproductora. En consecuencia, la composición óptima de la pollada probablemente varía en cada estación. Una vez identificado de sexo de los pollos mediante técnicas moleculares, encontramos que el sexo de la progenie estuvo influenciado por la interacción entre la fecha de eclosión y el orden de eclosión, de modo que la proporción de machos en los huevos eclosionados en tercer lugar incrementó inicialmente y luego disminuyó al final de la estación.

The Relationship between Egg Size and Chick Size in the Laughing Gull and Japanese Quail

Variation in the water, lipid, and nonlipid dry matter of eggs and newly hatched chicks of the Laughing Gull and Japanese Quail was related to variation in the size of the egg. Egg contents of the two species were, on average, very similar. Yolk size varied in direct proportion to egg size, but in the quail large eggs contained disproportionately low levels of lipid and high levels of nonlipid dry matter. The composition of the newly hatched gull chick closely resembled that of the newly hatched quail. With increasing egg size, and thus chick size, water level increased and lipid level decreased in the gull chick, whereas lipid level increased in the quail chick. Among body organs, the integument of the gull exhibited a disproportionate increase with an increase in egg size, owing mostly to the accumulation of water; in the quail, the legs were the only organs to increase out of proportion to increase in body size. Disproportionate decreases in body proportion with increasing chick size appeared mostly in the head, stomach, and intestine components of both species. Variation in proportions of lipid and water in the chick related to egg size is discussed in terms of (1) ecological requirements of newly hatched chicks, (2) sibling competition within broods, and (3) stage of development of the young at hatching.