Early Breeding Phase Research Articles

Behavioural plasticity in the early breeding season of pelagic seabirds - a case study of thin-billed prions from two oceans

BackgroundIn long-lived seabirds that migrate large distances independently of each other, the early part of the breeding season is crucially important for a successful reproductive attempt. During this phase, pair bonds are re-established and partners coordinate their breeding duties. We studied the early breeding season in Thin-billed prions Pachyptila belcheri breeding in the Atlantic Ocean (Falkland/Malvinas Islands) and Indian Ocean (Kerguelen). Despite overlap in the wintering areas, these two populations exhibit differences in their timing and direction of migration. We hypothesised that these differences would influence behaviour during the early breeding season.ResultsIn line with our hypothesis, we found very strong differences in colony attendance patterns. Thin-billed prions of the Falkland population spent the late winter period over shelf waters close to the colony, first arrived back at the colony in September, and attended the nests interruptedly for one month, before departing on a pre-laying exodus. In contrast, Kerguelen birds remained in the non-breeding areas until mid-October and spent much less time attending the burrow before their pre-laying exodus. Despite this asynchronous arrival to the two colonies, the subsequent patterns resulted in remarkably synchronous incubation in both populations, with males taking on the first long incubation shift in late November, whereas females returned to sea soon after egg laying. During the pre-laying exodus and incubation, Thin-billed prions from the Falklands spread north over the Patagonian Shelf, while prions from Kerguelen travelled much further, reaching southern oceanic waters and moved at faster speeds (> 400 km per day). Although prions from Kerguelen moved much further, their isotopic niches were considerably narrower, suggesting a stronger dependence on Antarctic waters.ConclusionsThe study thus suggests that Thin-billed prions show a high intraspecific plasticity in their use of either neritic or oceanic waters during the early breeding season. Breeding birds from the Falkland Islands can exploit an extensive shelf area, while Kerguelen birds have adapted to the need to forage in distant southern open waters. This difference in foraging ecology may thus have shaped the phenology of the early breeding phase.

Foraging Habitat Use of Oriental White Stork (Ciconia boyciana) Recently Breeding in China

The Yellow River Delta, a stopover site, has become one of the breeding sites of oriental white storks (Ciconia boyciana) in China, with 28 breeding pairs. To gain insight into the characteristics of foraging habitat use during the breeding season, we surveyed the foraging habitats in 2009 and 2010. In 2009, using a quadrat sampling technique, we surveyed 74 quadrats in two breeding phases. Fourteen variables were analyzed with DCA. Oriental white storks mainly foraged in the reed swamp of recovered wetlands during the early breeding phase (70.29%), and in the reed swamp of unrecovered area during the late phase (32.74%), and in the open water of recovered wetlands (29.95%). The variation in proportional habitat use was not significant in the two breeding phases. Differences of the foraging sites in the two phases were extremely significant in terms of plant density, distance from nest, and distance from highway. In 2010, the storks also mainly used the reed wetlands for foraging (87.00%). The top three parameters on the first axis with the highest scores were distance from nest, plant height, plant coverage; on the second axis, the top three variables with the highest scores were plant density, number of other waterbird species, and water depth. These results showed that there are differences in the foraging habitat use of oriental white storks in the early and the late breeding phases. It is favorable for the breeding of oriental white storks to recover the reed wetland and to preserve a certain area of open water habitats.

Testosterone Affects Song Modulation during Simulated Territorial Intrusions in Male Black Redstarts (Phoenicurus ochruros)

Although it has been suggested that testosterone plays an important role in resource allocation for competitive behavior, details of the interplay between testosterone, territorial aggression and signal plasticity are largely unknown. Therefore, we investigated if testosterone acts specifically on signals that communicate the motivation or ability of individuals to engage in competitive situations in a natural context. We studied the black redstart, a territorial songbird species, during two different life-cycle stages, the early breeding phase in spring and the non-breeding phase in fall. Male territory holders were implanted with the androgen receptor blocker flutamide (Flut) and the aromatase inhibitor letrozole (Let) to inhibit the action of testosterone and its estrogenic metabolites. Controls received a placebo treatment. Three days after implantation birds were challenged with a simulated territorial intrusion (STI). Song was recorded before, during and after the challenge. In spring, both treatment groups increased the number of elements sung in parts of their song in response to the STI. However, Flut/Let-implanted males reacted to the STI with a decreased maximum acoustic frequency of one song part, while placebo-implanted males did not. Instead, placebo-implanted males sang the atonal part of their song with a broader frequency range. Furthermore, placebo-, but not Flut/Let-implanted males, sang shorter songs with shorter pauses between parts in the STIs. During simulated intrusions in fall, when testosterone levels are naturally low in this species, males of both treatment groups sang similar to Flut/Let-implanted males during breeding. The results suggest that song sung during a territorial encounter is of higher competitive value than song sung in an undisturbed situation and may, therefore, convey information about the motivation or quality of the territory holder. We conclude that testosterone facilitates context-dependent changes in song structures that may be honest signals of male quality in black redstarts.

Genome-Wide Haplotype Changes Produced by Artificial Selection during Modern Rice Breeding in Japan

During the last 90 years, the breeding of rice has delivered cultivars with improved agronomic and economic characteristics. Crossing of different lines and successive artificial selection of progeny based on their phenotypes have changed the chromosomal constitution of the ancestors of modern rice; however, the nature of these changes is unclear. The recent accumulation of data for genome-wide single-nucleotide polymorphisms (SNPs) in rice has allowed us to investigate the change in haplotype structure and composition. To assess the impact of these changes during modern breeding, we studied 177 Japanese rice accessions, which were categorized into three groups: landraces, improved cultivars developed from 1931 to 1974 (the early breeding phase), and improved cultivars developed from 1975 to 2005 (the late breeding phase). Phylogenetic tree and structure analysis indicated genetic differentiation between non-irrigated (upland) and irrigated (lowland) rice groups as well as genetic structuring within the irrigated rice group that corresponded to the existence of three subgroups. Pedigree analysis revealed that a limited number of landraces and cultivars was used for breeding at the beginning of the period of systematic breeding and that 11 landraces accounted for 70% of the ancestors of the modern improved cultivars. The values for linkage disequilibrium estimated from SNP alleles and the haplotype diversity determined from consecutive alleles in five-SNP windows indicated that haplotype blocks became less diverse over time as a result of the breeding process. A decrease in haplotype diversity, caused by a reduced number of polymorphisms in the haplotype blocks, was observed in several chromosomal regions. However, our results also indicate that new haplotype polymorphisms have been generated across the genome during the breeding process. These findings will facilitate our understanding of the association between particular haplotypes and desirable phenotypes in modern Japanese rice cultivars.

Adjusting the timing of hatching to changing environmental conditions has fitness costs in blue tits

After laying the first egg, a bird can, to a certain extent, adjust the hatching date of the brood to environmental conditions. However, costs of this adjustment have remained largely unexplored. We studied potential costs of hatching delay in a population of blue tits in southern Finland. We explored the factors underlying hatching delay and investigated the association between hatching delay, clutch hatchability and female body condition. Finally, we reciprocally cross-fostered a large number of broods irrespective of their experienced hatching delay to address possible downstream effects of hatching delay on developmental parameters in offspring. We found that hatching delay was associated with early laying dates and low mean temperatures during the egg-laying phase. Furthermore, we found evidence that delayed hatching negatively affected the breeding performance. Hatchability of the clutch was lowered and the breeding female was energetically impaired, resulting in smaller clutch sizes, lower female body mass at hatching and lowered survival of nestlings reared in nests that had experienced a long hatching delay. In addition, delayed hatching had a significant negative effect on the body mass of nestlings prior to fledging. However, ultimately we did not find evidence that delayed hatching affected survival of the breeding female nor recruitment of fledglings in the local breeding population. Our study demonstrates that environmental conditions during egg laying can have lasting effects throughout the breeding and nestling phase. Furthermore, our results emphasize the importance of energetic tradeoffs by breeding females during the early breeding phase to manage reproductive costs.

Trade-off between migration and reproduction: does a high workload affect body condition and reproductive state?

Migratory birds have to invest much energy into flight to reach their summer and winter quarters. Many studies have shown how affects body physiology, including the accumulation of energy stores and the reduction of nonessential organs. In spring, the costs of may trade-off with preparations for breeding, such as the timing and extent of development of primary and secondary sexual traits. Birds arriving earlier on the breeding grounds often have a higher reproductive success than late-arriving birds, but no study to date has addressed whether and how the flight workload during itself influences reproduction. Using a wind tunnel, we investigated the effect of a high workload during long flights on measures of body condition and reproductive state in male rose-colored starlings (Sturnus roseus). We compared an experimental group that flew in the wind tunnel every day and covered a total flight distance of > 4700 km in 49 days with a control group of males that did not fly. All birds had ad lib access to food. After the migration period, individuals from both groups were kept in a common breeding aviary, where they directly competed for nest-boxes and females. Contrary to expectation, birds from the experimental and control group did not differ significantly in the spontaneous seasonal changes in fat score, in breast muscle thickness, in plasma testosterone levels, and in bill and mantle color. Body mass increased more slowly in experimental than in control birds, but it reached the same level soon after the period. We did not observe any effect of the experimentally increased heavy workload on behavior during the early breeding phase or on any parameter of reproductive success. We thus failed to find a trade-off between long flight and the development of traits in preparation for breeding or reproductive success. A possible treatment effect might have been obscured by the unrestricted food supply. However, we cannot exclude effects on other life-history stages such as future survival, migration, or reproduction. Our results attest to the strong endogenous control of seasonal physiological changes in preparation for breeding that occur independently of the extreme effort invested in long-distance migration.

The pineal clock affects behavioral circadian rhythms but not photoperiodic induction in the Indian weaver bird (Ploceus philippinus)

We investigated whether pineal is part of the circadian clock system which regulates circadian rhythms of activity and photosensitivity in the Indian weaver bird (Ploceus philippinus). Two experiments were performed. The first experiment examined the induction of testicular growth, and androgen-dependent beak pigmentation and luteinizing hormone (LH)-specific plumage coloration in pinealectomised (pinx) and sham-operated (sham) birds exposed to short day (8 h light: 16 h darkness, 8L:16D) and long day (16L:8D) for 9 months in the late breeding and early regressive phase (October), or the late regressive and preparatory phase (January) of the annual testicular cycle. As expected, short days were non-stimulatory, and long days stimulated testicular growth, beak pigmentation and plumage coloration. There was no difference in the response between pinx and sham birds subjected to short or long days in October, but the response was enhanced in pinx birds that were subjected to long day in January. In the second experiment circadian behavioral rhythms were studied (activity pattern in singly housed birds) in weaver birds first exposed at two different phases of the annual testicular cycle to a stimulatory photoperiod (12L:12D in preparatory phase or 13L:11D in early breeding phase) and then released into dim continuous light (LLdim). All birds showed synchronization to the light period before and after the pinealectomy; there was no difference in the response between pinx and sham birds. When released into LLdim, sham birds exhibited circadian rhythmicity continuously, whereas pinx birds lost circadian rhythmicity after some cycles. Considered together, these results suggest that circadian clock residing within the pineal gland regulates the circadian rhythm in activity, but not the circadian rhythm involved in photoperiodic induction of the Indian weaver bird.

Seasonal testicular cycle in a wild Indian Tree Pie Dendrocitta vagabunda.

Annual testicular activity was investigated in the Indian Tree Pie Dendrocitta vagabunda by studying the testis once a month throughout the year. The investigation revealed that testicular activity showed a distinct annual cycle consisting of four phases: nonbreeding (August to January); progressive (February and March); breeding (April and May); and regression (June and July). The testis weight, seminiferous tubular area and germ cell population were low during the nonbreeding phase, increased during the progressive phase, peaked during breeding and declined afterwards. But the sertoli cell population increased during the nonbreeding phase and decreased in the early breeding phase (April). The Leydig cells were large during the early breeding phase compared to other phases of the cycle. Cholesterol and ascorbic acid levels in the testis were highest during the nonbreeding phase, decreased moderately during the progressive phase, became lowest during the early breeding phase and began to rise thereafter. But acid phosphatase, alkaline phosphatase, sialic acid, RNA and protein content changes of the testis were the reverse. The findings indicate that the Indian Tree Pie has a single peak of spermatogenic activity in a year during April and May. Steroidgenic activity of the testis also varies with the spermatogenic cycle, but it appears to reach its peak slightly earlier in April than that of spermatogenic activity in this species.

Tail Regeneration in the Scincid Lizard, Mabuya carinata, related to Breeding Seasons and Thyroid Activity

The influence of two different seasons as well as of thyroid hormone on tail regeneration in Mabuya carinata has been evaluated by measuring the rate of growth of the regenerate at various time intervals. The analysis has revealed no apparent seasonal alteration in the final length attained at the end of 60 days. However, the average per day rate of growth indicates some difference between the late non-breeding and the early breeding phases. A better growth rate was noticeable in the non-breeding phase during the first 25 days (blastemic and differentiation phases) while it was better in the early breeding phase during the last 20 days of tail regeneration (late differentiation and growth phases). These observations correlate with the differential physiological and endocrine status characteristic of the two seasons. Hypothyroidic animals showed a 71% retardation of regenerative ability as compared to euthyroidic animals, which was however rectified by thyroxine replacement. Modes of action of thyroxine on lizard tail regeneration are discussed.