Gamete interaction: Is it species‐specific?

Reproductive isolation is pivotal to maintain species separation and it can be achieved through a plethora of mechanisms. In addition, the development of barriers to gamete interaction may drive speciation. Such barriers to interspecific gamete interaction can be prezygotic or postzygotic. Considering the great diversity in animal species, it is easy to assume that regulation of the early steps of fertilization is critical to maintain species identity. One prezygotic mechanism that is often mentioned in the literature is that gamete interaction is limited to gametes of the same species. But do gametes of all animals interact in a species‐specific way? Are gamete interactions completely species‐specific or perhaps just species‐restricted? In species in which species‐restrictions have been described, is the interspecies barrier at one major step in the fertilization process or is it a combination of partially restricted steps that together lead to a block in interspecific fertilization? Are the mechanisms used to avoid interspecific crosses different between free‐spawning organisms and those with internal fertilization? This review will address these questions, focusing on prezygotic barriers, and will describe what is known about the molecular biology that may account for species‐limited gamete recognition and fertilization. Mol. Reprod. Dev. 73: 1422–1429, 2006. © 2006 Wiley‐Liss, Inc.     

Pollen-Ovule Ratio and Gamete Investment in Pedicularis （Orobanchaceae）

The Pedicularis species provides ideal materials to study floral evolution because of their substantial flower variation based on a narrow genetic basis, even though they are almost exclusively pollinated by bumblebee. These traits allow us to detect the evolutionary trends of floral parameters without considering genetic background and the difference of pollination vectors. The pollen-ovule ratio is widely used to estimate the pattern of resource investment in two sexual functions in flowering plants. Forty species representing all of the corolla types in Pedicularls were used to study pollen-ovule ratio, gamete investment, and their correlations. Results show that pollen-ovule ratio does not differ among both different corolla types and taxonomic groups. It is therefore suggested that pollen-ovule ratio should be a parallel evolution. The correlations between pollen-ovule ratio and pollen size （-）, and ovule size （＋） can be successfully explained in terms of sex allocation theory. The biological significance of such relationships was also discussed. Additionally, we analyzed the pattern of resource investment into female gamete, which has been somewhat neglected, and found that plants have different patterns of gamete investment between the two sexual functions.     

Determination of n-l-1 Gamete Transmission Rate of Trisomics and Location of Gene Controlling 2n Gamete Formation in Chinese Cabbage （Brassica rapa）

A set of trisomics of Chinese cabbage was used for determining the n-I-1 gamete transmission rate and locating the gene controlling 2n gamete formation on the corresponding chromosome. The results showed that the transmission rates of extra chromosomes in different trisomics varied from 0% to 15.38% by male gametes and from 0% to 17.39% by female gametes. Of the nine F2 populations derived from the hybridizations between each trisomic and Bp058 （2n gamete material）, only Tri- 4xBp058 showed that the segregation ratio of plants without 2n gamete formation to plants with 2n gamete formation was 10.38：1, which fitted the expected segregation ratio of the trisomics （AAa） based on the 7.37% of n＋l gamete transmission through female and 5.88% through male. In other populations the segregation ratios varied from 2.48：1 to 3.72：1, which fitted the expected 3：1 segregation ratio of the bisomics （Aa）. These results suggested that the gene controlling 2n gamete formation in Chinese cabbage Bp058 was located on chromosome 4. Further trisomic analysis based on the chromosome segregation and the incomplete stochastic chromatid segregation indicated that the gene locus was tightly linked to the centromere.     

Organ Donation: Who Should Decide?—A Canadian Perspective

This paper examines an under-explored issue in organ donation: whose decision making authority should be privileged posthumously in the context of known, explicit consent for donation? Current practices in Canada support the family as the ultimate decision maker, despite the existence of legislative support in many Canadian provinces for the potential donor as legitimate decision maker. Arguments for and against privileging the family and the potential donor are identified. Informing the question of “who should decide” are considerations of individual and relational autonomy, distributive and social justice, personhood, and arguments “from distress”. Tensions and competing obligations emerge from an exploration of these considerations that call for further, inclusive dialogue and deliberation on this important organ donation issue.     

Gamete Release at Low Tide in Fucoid Algae: Maladaptive or Advantageous?

This review discusses three questions pertaining to gamete releaseby fucoid algae at low tide: 1) Are gametes viable and doesfertilization occur at low tide?, 2) How many gametes are releasedat low tide versus at high tide? and 3) Is gamete release atlow tide maladaptive or is it selectively advantageous? Gameterelease at low tide (LT) in fucoid algae is observed commonlyin monoecious species from the lower and mid-intertidal zones(e.g., Fucus distichus, F. evanescens, F. gardneri, Pelvetiacompressa); in dioecious species, intact antheridia (containingsperm) are commonly released at low tide (e.g., in Ascophyllumnodosum, F. vesiculosus). Fertilization at low tide can be determinedwith a calcofluor white assay and occurs in at least three species(F. distichus, F. gardneri, P. compressa). In general, fucoidalgae have high levels of fertilization success, but substantialmortality occurs during early embryogenesis in some intertidalzones due to physical stresses. The agarose bead assay is usefulto assess desiccation on an egg-sized scale. Constitutive dehydrin-likeproteins are present in sperm, eggs, and embryos. The releaseof gametes at low tide appears to be a consequence of a mechanismselected to permit gamete release under calm conditions in seawater;this mechanism is described. The timing of adhesion by zygotesat low and high tide is unknown. Such information and additionaldata on the relative proportions of zygotes produced by moneciousspecies at low tide versus high tide are required in order toassess effects of gamete release at low tide upon dispersaland population structure.     

Gamete formation via meiotic nuclear restitution generates fertile amphiploid F1 (oat?×?maize) plants

Hybrid (oat×maize) zygotes developed into euhaploid plants with complete oat chromosome complements without maize chromosomes and into aneuhaploid plants with complete oat chromosome complements and different numbers of retained individual maize chromosomes. The elimination of maize chromosomes in the hybrid embryo is caused by uniparental genome loss during early steps of embryogenesis. Some of these haploid plants set seed in up to 50% of their self-pollinated spikelets. The high fertility was found to be mainly caused by formation of numerically unreduced female and male gametes (nunreduced=3x+0…3=21…24 chromosomes). Gamete formation involves meiotic nuclear restitution. The restitution process is caused by an alternative type of meiosis. It follows the model of levigatum-type semi-heterotypic divisions, but with a formation of the nuclear membrane at the transition from telophase I to interkinesis, which resembles the model of pygaera-type pseudo-homotypic divisions. We propose the name haploid meiotic restitution for this particular process combination. We discuss the use and implications of the specific process of gamete formation in F1 (oat×maize) plants.     

The Sun Health Research Institute Brain Donation Program: Description and Eexperience, 1987–2007

The Brain Donation Program at Sun Health Research Institute has been in continual operation since 1987, with over 1000 brains banked. The population studied primarily resides in the retirement communities of northwest metropolitan Phoenix, Arizona. The Institute is affiliated with Sun Health, a nonprofit community-owned and operated health care provider. Subjects are enrolled prospectively to allow standardized clinical assessments during life. Funding comes primarily from competitive grants. The Program has made short postmortem brain retrieval a priority, with a 2.75-h median postmortem interval for the entire collection. This maximizes the utility of the resource for molecular studies; frozen tissue from approximately 82% of all cases is suitable for RNA studies. Studies performed in-house have shown that, even with very short postmortem intervals, increasing delays in brain retrieval adversely affect RNA integrity and that cerebrospinal fluid pH increases with postmortem interval but does not predict tissue viability.     

Creating Donors: The 2005 Swiss Law on Donation of ‘Spare’ Embryos to hESC Research

In November 2004, the Swiss population voted to accept a law on research using human embryonic stem cells. In this paper, we use Switzerland as a case study of the shaping of the ostensibly ethical debate on the use of embryos in embryonic stem cell research by legal, political and social constraints. We describe how the national and international context affected the content and wording of the law. We discuss the consequences of the revised law's separation of stem cell research from other forms of embryo research, its definitions of embryo and of spare embryos, and the introduction of donorship into the Swiss ethical debate on IVF. We focus on the exclusion of the potential embryo donors' voices and perspectives from the debate, and consider the effects of this exclusion on ethical discourse and the political process.     

Should We Formulate an Incentivized Model Facilitating Kidney Donation from Living Donors? A Focus on Turkey's Current System

Kidney transplantation is a lifesaving medical treatment. However, very high demand for kidneys with low kidney donation causes a black market that exploits patients’ desperation and donors’ vulnerability. The current kidney donation programs fail to produce promising results to avoid illegal and unethical kidney trafficking and commercialism. Even though the primary goal of kidney donation is to increase the number of deceased organ donations, in some countries, like Turkey, due to religious or cultural concerns, it is impossible to supply adequate deceased kidney donations. In this view, the aim of this paper is to examine kidney trafficking in the scope of Turkey's current organ donation system and propose a new model, named the Incentivized Kidney Donation Model (IKDM), to increase kidney donation from living donors. The model encompasses the following benefits offered to kidney donors; lifetime health insurance, exemptions from copayments/contribution shares, priority when receiving an organ, priority when finding a job, income tax exemptions for salaried employees, and free or discounted public utilities. This normative model has the potential to promote donors’ altruistic acts as well as the solidarity and loyalty among members of a society without violating ethical values and internationally accepted principles.