Local breeding experience and the reproductive performance of Tree Swallows

ABSTRACT The potential advantages of repeated breeding at a particular location should improve reproductive performance in long‐lived species of birds. However, for short‐lived species, natural selection should favor individuals that most quickly develop competency in reproduction. Therefore, we hypothesized that local breeding experience beyond the first breeding attempt at a particular location would have little effect on subsequent reproductive performance of Tree Swallows (Tachycineta bicolor), a species where about 50% of adults breed only once in their lives. We tested this hypothesis using data collected from Tree Swallows in Michigan from 1993 to 2002. Because we were specifically interested in examining the effects of local breeding experience on reproductive performance, we restricted our analyses to after‐second‐year (ASY) females and their mates that we first encountered as breeders. Consistent with our hypothesis, we found no relationship between repeated local breeding experience and the reproductive performance of ASY female Tree Swallows and their mates as measured by clutch size and number of fledged young. However, pairs with more combined total local experience tended to lay eggs earlier in the season. These results suggest that Tree Swallows may benefit from breeding site fidelity, not because repeated local experience improves reproductive performance as measured by the production of fledglings, but because returning individuals acquire nest cavities earlier and are able to begin breeding earlier, providing time to renest in case of early nest failure.     

SPORELING COALESCENCE AND INTRACLONAL VARIATION IN GRACILARIA CHILENSIS (GRACILARIALES,RHODOPHYTA)1

This study evaluates the hypothesis that spore coalescence may cause intraclonal variation. Spore coalescence might allow the occurrence of unitary thalli that in fact correspond to genetically different, coalesced individuals. Plant portions simultaneously derived from these chimeric individuals may exhibit dissimilar growth responses even when incubated under similar abiotic conditions. Testing of the hypothesis included various approaches. Transmission electron microscopy observations of early stages of sporeling coalescence indicated that polysporic plantlets were formed by groups of spores and their derivatives. Even though adjacent cells in two different groups may fuse, these groups maintained an independent capacity to grow and form uprights. Laboratory-grown plantlets showed a significant correlation between the initial number of spores and the total number of erect axes differentiated from the sporeling. Construction and growth of bicolor individuals indicated the chimeric nature of the coalesced individuals. Coalesced, bicolor holdfasts had green and red cells, which subsequently produced green and red uprights, respectively. Individuals fronds were also chimeric, as indicated by the production of green and red branchlets from single, red uprights. The existence of mixed tissues was further substantiated by random amplified polymorphic DNA analysis. The banding pattern produced by branchlets of a unisporic thallus was consistently monomorphic, whereas the patterns produced by the polysporic thallus were polymorphic. Growth rates of polysporic thalli had larger data dispersal and variation coefficients than oligosporic or monosporic thalli. Therefore, all results support the original hypothesis and suggest that coalescence might be ecologically more important than previously thought.     

紫背菜的食用价值及其开发利用前景

紫背菜的生物学与生态学特性、病虫害防治、营养成分、药用价值及其综合开发利用方面的研究表明:紫背菜及其色素提取物等营养成分在治疗糖尿病等人类疾病及食品加工等领域的综合开发利用前景广阔。     

Repeatability of extra-pair mating in tree swallows

Models of sexual selection assume that female mating preferences are heritable and, thus, repeatable for individual females across multiple mating episodes. Previous studies of the repeatability of female preference have examined individuals in captivity and focused presumably on social mate choice. However, extra-pair mating is widespread and can also influence sexual selection. We examined the repeatability of extra-pair mating in a wild population of tree swallows (Tachycineta bicolor) by experimentally inducing females to lay two clutches in rapid succession within the same season. We found that the proportion of extra-pair young and the number of extra-pair sires were highly repeatable for individual females. However, the repeatability of specific extra-pair sires was low. We suggest that this unusual pattern of mating may be due to females maximizing the heterozygosity of their offspring.     

Genetic transformation of Sorghum bicolor

Great millet (Sorghum bicolor (L.) Moench) is cultivated across the world for food and fodder. It is typically grown in semiarid regions that are not suitable for cultivation of other major cereals. Sexual incompatibility and shortage of available genes in germplasm to combat biotic and abiotic stresses resulted in marginalized yields of this crop. Genetic modification of sorghum with agronomically useful genes can address this problem. Here, we tried to review and summarize the key aspects of sorghum transformation work being carried out so far by various research groups across the world. The approaches used and the obstacles in generating transgenic sorghum are also pointed out and discussed.     

红凤菜和白子菜总黄酮含量的动态变化

红凤菜[Gynura bicolor (Willd. ) DC. ]和白子菜[G. divaricata (L. ) DC. ]均为菊三七属(Gynura Cass. )植物~([1]).红凤菜的嫩茎叶中含有丰富的营养成分,可作蔬菜食用~([2]);白子菜叶片在民间用于治疗糖尿病,动物实验证明其有显著的降血糖作用~([3]).     

NaCl对中华补血草叶片盐腺发育及其泌盐速率的影响

以中华补血草(Limonium sinenseKuntze)为实验材料,研究了不同浓度NaCl处理对其生长、盐腺发育及泌盐速率的影响.结果显示:(1)随着NaCl浓度的升高,植株干重和鲜重均先显著升高后逐渐下降,当NaCl处理浓度为100 mmol/L时,植株干、鲜重达到最大;(2)与对照相比,300 mmol/L NaCl处理下盐腺的分泌细胞及平均直径差异不显著,而在1002、00 mmol/L的NaCl处理下显著增大;(3)随着NaCl浓度的升高,盐腺密度显著升高且叶片上表面盐腺总数明显高于对照,单个盐腺的泌盐速率和叶片整体泌盐速率均显著升高.结果表明,100~200 mmol/L NaCl处理可显著促进中华补血草盐腺的发育及泌盐能力,300 mmol/L以上NaCl处理对盐腺的直径影响不显著,但可显著促进盐腺的泌盐能力.     

Age and growth of Anguilla bicolor bicolor leptocephali in the eastern Indian Ocean

A sampling survey for leptocephali was conducted in the eastern Indian Ocean to the west of Sumatra from 5 to 20 June 2003 in an overlapping area with the historical survey in September to November 1929 during the Danish Round the World Expedition. The age and larval growth rate of 34 Anguilla bicolor bicolor collected in 2003 were estimated using their otolith microstructure to obtain new information about the early life history of this sub-species. The total lengths and ages of these leptocephali were 44·1–55·5 mm and 114–158 days, respectively. Their hatching dates ranged from 3 January to 20 February 2003. Combining these age data and the estimated age of leptocephali collected by others in the same area, this sub-species was estimated to have a wide range of spawning periods. Individual growth rates of the leptocephali in 2003 ranged from 0·32 to 0·39 mm day⁻¹ with a mean ± s . d . of 0·35 ± 0·02 mm day⁻¹. These values were lower than the growth rates of leptocephali of other tropical eels such as Anguilla celebesensis or Anguilla borneensis , suggesting that A. b. bicolor from the eastern Indian Ocean have a longer leptocephalus period of oceanic migration.