Male brood provisioning rates provide evidence for inter‐age competition for mates in female Cooper's Hawks Accipiter cooperii

Life history theory predicts that individuals should maximize lifetime reproductive success (LRS) by breeding as soon as they reach sexual maturity, yet many species delay breeding, either because there are insufficient available mates or breeding sites, or because delayed breeding yields higher LRS. Accipitriform species, such as Cooper's Hawk Accipiter cooperii, exhibit both delayed breeding and delayed plumage maturation. However, in certain circumstances, first‐year females in non‐definitive plumage do breed and apparently compete with older females for high‐quality breeding territories. We predicted that these young females are at a competitive disadvantage compared with older females and that older females would have both higher reproductive success and be able to acquire higher quality nesting territories. We conducted brood counts and measured prey delivery rates by male Cooper's Hawks in an expanding urban population located in Albuquerque, New Mexico (USA), to assess our prediction. We found that older females had higher reproductive success, fledging 1.6 more offspring than younger females, and that they occupied territories where males provisioned at higher rates of 0.37 more prey items per 2‐h period. Our results showed that older females fared better than first‐year females but it is unclear if this is the result of passive or active competition. Older females initiated nesting 14.3 days sooner than first‐year females and thus may have filled vacant, high‐quality territories before first‐year females began seeking mates. Additionally, first‐year females were never observed persistently to confront older females for breeding territories, but they did actively compete against each other. First‐year females may defer to older females who, in a direct competitive interaction, would be most likely to prevail. Thus, delayed plumage maturation in Cooper's Hawks may serve to focus competition for nesting territories within age classes.     

大果白刺雄性不育系的细胞学研究

利用石蜡切片法对大果白刺花药进行细胞学研究,探讨雄性不育系发生败育的时期和方式以及雄性败育与药壁组织间的关系.结果表明:不育系小孢子母细胞形成前期,花药各部分结构发育正常.随着绒毡层的异常解体,多种异常现象相继出现,包括小孢子母细胞液泡化,中层、药室内壁、药隔细胞液泡化,细胞畸形,药壁细胞非正常解体等.退化后整个花药萎缩干瘪,不能开裂,无花粉.因此,大果白刺雄性不育系的绒毡层生理异常并提前退化是导致雄性不育的主要原因.     

Predator avoidance behaviour in wild and hatchery‐reared brown trout: the role of experience and domestication

Juvenile brown trout Salmo trutta from natural populations reacted to the presence of piscivorous brown trout by increasing the use of refuges. In contrast, second‐generation hatchery fish and the offspring of wild fish raised under hatchery conditions were insensitive to predation risk. The diel pattern of activity also differed between wild and hatchery brown trout. Second‐generation hatchery fish were predominantly active during daytime regardless of risk levels. Wild fish, however, showed a shift towards nocturnal activity in the presence of predators. These findings emphasize the potential role of domestication in weakening behavioural defences. They support the idea that the behavioural divergence between wild and domesticated individuals can arise from a process of direct or indirect selection on reduced responsiveness to predation risk, or as a lack of previous experience with predators.     

Comparative Developmental Study of the Evolutionary Reduction of Adaxial Microsporangia in Microseris bigelovii (Asteraceae)

Abstract: About 10% of all angiosperm species have only 2 pollen sacs (microsporangia) per anther in place of the normal 4. The reduction seems to have occurred independently in about 50 angiosperm families and is a prime example of the parallel evolution of a potentially diagnostic taxonomic character (homoplasy). In the genus Microseris reduction from 4 to 2 mi-croporangia (MS) is a synapomorphy for three of the diploid annual species. We have compared anther development in the tet-rasporangiate (4MS) M. douglasii with that in the disporangiate (2MS) M. bigelovii . In this case, the divergence between the developmental pathways becomes visible late in ontogeny, when the adaxial archesporial cells divide into primary parietal cells and sporogenous cells. In the disporangiate M. bigelovii this differentiation step is lacking so that no adaxial MS are formed. Anther development in a recombinant inbred derivative of a hybrid between M. douglasii and M. bigelovii resulted in the formation of sterile adaxial MS. This suggests a two-step evolution of the character: suppression of the differentiation of fertile cells in otherwise normal adaxial loculi followed by the suppression of the production of sterile precursors. Comparison with other cases of evolutionary reduction of microsporangia suggests that there are (many) different ways to reach the same stable ("canalized") phenotype. This may be generally true for homoplasy in complex developmental characters.     

Histology of embryogenic responses in soybean anther culture

In order to clarify the embryogenic responses in soybean anther culture, anthers of four cultivars were cultured under known conditions to trigger androgenic response. A histological study was performed with anthers in vivo and with approximately 100 explants sampled after 9, 12, 15, 18, 21, 30 and 45 days of culture. In vitro culture triggered the frequent accumulation of phenolic compounds on the locular and anther surfaces, and also caused the destruction of cells and tissues in complex structure such as the tapetum, microspores and pollen grains. Somatic embryogenesis of unicellular origin was observed from the epidermis and the middle layer, and of multicellular origin from connective calluses. No androgenic response could be observed in the anthers of these four soybean genotypes, in the medium and conditions indicated. We point out to the need of changing the approach to the study of androgenesis in soybean, either by using culture conditions unfavourable to the proliferation of diploid tissues, or by culturing isolated microspores.     

Meiotic metaphase I to telophase II as the most responsive stage during microspore development for callus induction in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>) anther cultures

The generation of homozygous doubled haploid lines through induction of androgenesis is a promising alternative to the classical inbreeding and selection programs. However, this technology is poorly developed in tomato, where doubled haploid tomato plants have only been obtained through anther culture. Despite the fact that anther culture is routinely used in a number of economically interesting crops, there are still many drawbacks that prevent tomato breeders from adopting this technique, and improvements in methodology are required. One key issue is the correct identification of the optimal stage for anther excision and culture. In this paper we characterise in vivo microsporogenesis in tomato, defining the different microspore stages and relating them to the length of the donor flower bud. In parallel, we cultured anthers of these stages to obtain embryogenic callus, and followed the microscopic development of the callus contained within the anther. Our data suggest that the stage with the highest response, in terms of callus generation, is meiosis. In particular, we propose the window from metaphase I to telophase II, including tetrad cellularisation, as the timeframe where induction can be accomplished in tomato anther cultures.     

Anther Culture Response of Barley Genotypes to Cold Pretreatments and Culture Media

The embryoid formation and plant regeneration in anther cultures of three barley (Hordeum vulgare L.) cultivars (Niki, Karina, Thermi), one F₁ hybrid (Niki × Thermi), two F₂ populations (Niki × Thermi, Niki × Karina), and two F₃ populations (Niki × Thermi, Niki × Karina) were investigated in two solid induction media after cold pretreatment for 14 and 28 days at 4°C . The media used (N6 and FHG) differed in their composition and source of energy (maltose in FHG vs. sucrose in N6). Embryoid frequency and green plant regeneration depended on both the induction medium composition and cold pretreatment. The combination of the FHG induction medium with 28-day-long cold pretreatment was the most efficient in haploid embryoid formation and green plant production. In addition, the green plant production was genotype-dependent. Cv. Thermi and F₁ hybrid Niki × Thermi exhibited the highest frequency of green plant production. The parent with high or even moderate frequency of embryoid formation in anther culture could lead to the effective production of green plants from the F₁ hybrid or the F₂ generation for breeding purposes.     

Surprising Effects of Synaptic Excitation

Typically, excitatory synaptic coupling is thought of as an influence that accelerates and propagates firing in neuronal networks. This paper reviews recent results explaining how, contrary to these expectations, the presence of excitatory synaptic coupling can drastically slow oscillations in a network and how localized, sustained activity can arise in a network with purely excitatory coupling, without sustained inputs. These two effects stem from interactions of excitatory coupling with two different forms of intrinsic neuronal dynamics, and both serve to highlight the fact that the influence of synaptic coupling in a network depends strongly on the intrinsic properties of cells in the network.This work was partially supported by the National Science Foundation, under award DMS-0414023     

The use of mutagens to increase the efficiency of the androgenic progeny production in <Emphasis Type="Italic">Solanum nigrum</Emphasis>

Pollen embryogenesis was successfully induced in Solanum nigrum L. (2n=6×=72). Stimulation of androgenesis expressed as the frequency of androgenic responsive anthers was observed after 10 and 20 mM ethyl methanesulphonate (EMS), 10 and 20 mM sodium azide (NaN₃) and 0.2 mM N-nitroso-N-methylurea (MNU) treatment applied on seeds for 24 h. The frequency of androgenesis on the medium with sucrose was higher than on the medium with maltose. Androgenic regenerants originated also in the anthers collected from donor plants where survival after mutagenic treatment was lower than 50 %. Green haploid (3x), aneuploid (to 8x) and dihaploid (6x) plants were obtained. The high frequency of aneuploids among androgenic plants is explained by cell division irregularities in microsporial calli.