Male death resulting from hybridization between subspecies of the gypsy moth,Lymantria dispar

We explored the origin of all-female broods resulting from male death in a Hokkaido population of Lymantria dispar through genetic crosses based on the earlier experiments done by Goldschmidt and by testing for the presence of endosymbionts that are known to cause male killing in some insect species. The mitochondrial DNA haplotypes of the all-female broods in Hokkaido were different from those of normal Hokkaido females and were the same as those widely distributed in Asia, including Tokyo (TK). Goldschmidt obtained all-female broods through backcrossing, that is, F1 females obtained by a cross between TK females (L. dispar japonica) and Hokkaido males (L. dispar praeterea) mated with Hokkaido males. He also obtained all-male broods by mating Hokkaido females with TK males. Goldschmidt inferred that female- and male-determining factors were weakest in the Hokkaido subspecies and stronger in the Honshu (TK) subspecies. According to his theory, the females of all-female broods mated with Honshu males should produce normal sex-ratio broods, whereas weaker Hokkaido sexes would be expected to disappear in F1 or F2 generations after crossing with the Honshu subspecies. We confirmed both of Goldschmidt''s results: in the case of all-female broods mated with Honshu males, normal sex-ratio broods were produced, but we obtained only all-female broods in the Goldschmidt backcross and obtained an all-male brood in the F1 generation of a Hokkaido female crossed with a TK male. We found no endosymbionts in all-female broods by 4,′6-diamidino-2-phenylindole (DAPI) staining. Therefore, the all-female broods observed in L. dispar are caused by some incompatibilities between Honshu and Hokkaido subspecies.     

Local Mating,Dispersal and Sex Ratio in a Gregarious Parasitoid Wasp

Parasitoid sex ratios can be greatly influenced by mating and dispersal behaviour. Many sex ratio models assume that mating is strictly local (only mated females disperse from the natal patch) and that a single male is sufficient to inseminate all females in a brood. Bethylids (aculeate parasitoids) have been used to test predictions of these models, but less attention has been paid to testing their underlying assumptions. We investigated the timing of eclosion, mating and dispersal in mixed-sex and single-sex broods of the bethylid wasp Goniozus nephantidis. In mixed-sex broods, almost all females mate before dispersal and a single male is sufficient to inseminate virtually all females, even when brood sizes are large. Males disperse from both mixed-sex and all-male broods, but males in all-male broods disperse more slowly. Virgin females disperse from all-female broods, which are common. Virgin females can produce a brood, mate with their own sons and subsequently produce mixed-sex broods, but their success rate is very low. Virgin females could potentially circumvent sex allocation constraints by superparasitizing mixed-sex broods, but when presented with hosts bearing mixed-sex broods they destroy all members of the initial brood before ovipositing. Because of the high prevalence of single-sex broods and dispersal of both sexes, the mating structure of G. nephantidis is unlikely to conform to the assumption of strict local mating.     

Phylogenetic relationships among bisexual and unisexual lineages of the weevil Scepticus insularis (Coleoptera: Curculionidae) on Hokkaido, Northern Japan

We examined the geographic distributions and phylogenetic relationships of bisexual and unisexual (parthenogenetic) forms of the weevil Scepticus insularis on Hokkaido Island, northern Japan. Unisexual beetles were widespread throughout Hokkaido, whereas bisexuals were found only in three remote areas. Bisexuals (females and males) and unisexual females occurred sympatrically in two areas. We determined nucleotide sequences for part of the mitochondrial NADH dehydrogenase subunit 2 (ND2; 633 bp) gene for 104 individuals, and for part of the nuclear internal transcribed spacer region 2 (ITS2; 360 bp) for 91 individuals. In an ND2 gene tree, haplotypes of S. insularis fell into two distinct clades (A and B), which were genetically differentiated from one another by 9.1% nucleotide sequence divergence. Haplotypes of females identified as unisexual were all in clade A, whereas those of females identified as bisexual belonged to clade B. Haplotypes of males were in clade B, except for two males having a clade-A haplotype. Circumstantial evidence suggests that these two males were produced by unisexual females. The ND2 tree suggests that the current unisexual form of S. insularis on Hokkaido was of a single origin. In contrast, a gene tree for ITS2 haplotypes show no clear divergence between the two modes of reproduction, with two major haplotypes shared by unisexual females, bisexual females, and males. This incongruence between the nuclear and mitochondrial phylogenies may be attributable to occasional gene flow between the unisexual and bisexual lineages through males occasionally produced by unisexual females, but our results do not exclude the possibility that the two lineages share polymorphic ancestral ITS2 haplotypes.     

Hatching order and size-dependent mortality in relation to brood sex ratio composition in chinstrap penguins

The differential environmental sensitivity of the sexes hasstrong implications in the evolutionary history of species asit can alter sexual size dimorphism, population sex ratios,and the faculty of parents to manipulate offspring sex in relationto environmental conditions. We studied sexual differences inhatching patterns and evaluated sex- and size-related mortalityin relation to hatching order and brood sex ratios in the chinstrappenguin Pygoscelis antarctica, a moderately size-dimorphic species,with a modal clutch size of 2 eggs. We found that male, second-hatched,and large eggs showed shorter hatching periods than female,first-hatched, and small eggs. We also found a male-biased mortalityof nestlings in the colony. However, male mortality patternsdiffered depending on the brood sex ratio composition. Mortalityof male chicks in all-male broods was higher than in mixed broodsand higher than female mortality in all-female broods. Contrary,females from mixed brood showed higher mortality than theirmale nest mates and higher too than females in all-female broods.Second-hatched chicks also suffered from higher mortality thanfirst-hatched chicks. Our results indicate that both the superiorcompetitive capacity and the higher energy demand of the largersex constitute 2 causal factors explaining patterns of sex-biasedmortality. Both factors occur in the same species and in differentsituations of sibling competition shaped by brood sex ratiocomposition. This study constitutes a good example of how patternsof sex-related mortality can vary depending on nest environmentalcircumstances. Furthermore, our study suggests that hatchingperiod can be a mechanism underlying sexual differences in theembryonic period of birds.     

Brood sex ratio variance,developmental mortality and virginity in a gregarious parasitoid wasp

Females of the parasitoid wasp Goniozus nephantidis paralyse host caterpillars and lay a clutch of up to 18 eggs onto the host integument. The known biology of G. nephantidis suggests that matings occur exclusively between siblings from the same brood. This leads to the prediction that brood sex ratios should be highly female-biased and have low variance. Sex ratios are indeed female-biased, with the mean proportion of males equal to 0.093. However, while sex ratio variance is significantly less than binomial, many broods contain no males at emergence. During development 28% of G. nephantidis offspring die. Male mortality offers a potential explanation for all-female (= virgin) broods. For the clutch sizes and mortality observed, theory predicts that <10% of females will emerge from all-female broods but the empirical value is much higher. The prediction that the prevalence of virginity decreases with increasing clutch size is, however, supported. We consider alternative explanations for the observed proportion of all-female broods, but this appears to be neither an artefact of the laboratory environment nor due to incorrect assumptions about G. nephantidis life history. Although its reproductive biology has been much investigated and its sex ratio matches some theoretical predictions, we conclude that a fuller understanding of G. nephantidis sex ratio requires a deeper knowledge of its field biology.     

Multiple parthenoforms of Empoasca leafhoppers from Madeira Island: where are these unisexual forms coming from?

There are controversial opinions on whether asexual reproduction is more common on islands than on the mainland. Although some authors consider that the evidences of geographical parthenogenesis support the view that asexual reproduction is more common on islands, comparative data on the modes of reproduction of insular and continental taxa confirming this statement are very limited. In this work, we report the presence of three unisexual forms and three bisexual species of the genus Empoasca (Cicadelloidea, Hemiptera, Insecta) from Madeira Island. Experimentally, the unisexual forms reproduced in the absence of males for several generations. The chromosome analysis has shown that the bisexual species differ from one another in chromosome number, and unisexual forms are apomictic and also each have different chromosome numbers. Of parthenoforms, one is triploid and two are of obscure level of ploidy, 2n or 3n. The results obtained show that for this genus unisexual forms are more common on Madeira Island than in the nearby continental areas. It is suggested that unisexual forms may be more plentiful on islands than on the mainland because if an asexual reproduction event occurs, the relaxing competition in these underexploited and enemy-free habitats may favor the establishment of new parthenogenetic lineages.     

Evidence for a priming effect on maternal resource allocation: implications for interbrood competition

It is commonly assumed that there exists interbrood competition mediated by in utero growth. This could be manifested by a female reallocating saved resources to future broods. Here, we report results of a manipulation experiment designed to detect such reallocation. Two groups of female mice were allowed each to produce two broods. In the first brood, the test females were mated with phenotypically normal males heterozygous for an insulin-like growth factor 2 (Igf2) null allele, while the control females were mated to a wild-type male. The test sample females invested 20% less into their first brood than did the control sample. In both test and control groups the females were mated with a wild-type male in the second round of mating. Surprisingly, we found that females that invested little into their first brood also invested little (compared with other second broods) into their second brood. This 'priming' effect suggests that the assumptions of classical models of parent-offspring conflict are overly simplistic but cannot disprove the existence of interbrood competition.     

Hatching asynchrony and brood reduction influence immune response in Common Kestrel Falco tinnunculus nestlings

The onset of incubation before the end of laying imposes asynchrony at hatching and, therefore, a size hierarchy in the brood. It has been argued that hatching asynchrony might be a strategy to improve reproductive output in terms of quality or quantity of offspring. However, little is known about the mediating effect of hatching asynchrony on offspring quality when brood reduction occurs. Here, we investigate the relationship between phenotypic quality and hatching asynchrony in Common Kestrel Falco tinnunculus nestlings in Spain. Hatching asynchrony did not increase breeding success or nestling quality. Furthermore, hatching asynchrony and brood reduction had different effects on nestlings’ phytohaematogglutinin (PHA)‐mediated immune response and nestling growth. In asynchronous and reduced broods (in which at least one nestling died), nestlings showed a stronger PHA‐mediated immune response and tended to have a smaller body size compared with nestlings raised in synchronous and reduced broods. When brood reduction occurred in broods hatched synchronously, there was no effect on nestling size, but nestlings had a relatively poor PHA‐mediated immune response compared with nestlings raised in asynchronous and reduced broods. We suggest that resources for growth can be directed to immune function only in asynchronously hatched broods, resulting in improved nestling quality, as suggested by their immune response. We also found that males produced a greater PHA‐mediated immune response than females only in brood‐reduced nests without any effect on nestling size or condition, suggesting that females may trade off immune activities and body condition, size or weight. Overall, our results suggest that hatching pattern and brood reduction may mediate resource allocation to different fitness traits. They also highlight that the resolution of immune‐related trade‐offs when brood reduction occurs may differ between male and female nestlings.     

Weight loss of the female during the first brood as a factor influencing second brood initiation in Great Tits Parus major and Blue Tits P. caeruleus

We tested the hypothesis that the weight lost by female Great and Blue Tits Parus major and P. caeruleus while raising their first brood influences their ability to start a second brood. The evening weight of female parents was recorded when the nestlings were 5 and 13 days old, in different years and habitats. Several predictions were tested: (1) both species lose weight while raising nestlings and Great Tit females which start a second brood lose less weight than females which do not; (2) differences in the average weight lost between years and areas correlate with differences in the proportion of second broods; (3) the relative weight loss in Blue Tits, which only rarely undertake second broods, is higher than in Great Tits in which second broods are more common. Other factors also are related to the probability of undertaking a second brood: more second broods are undertaken by more successful females, adult females and females that lay earlier.
The comparison of Great and Blue Tits suggests that the two species use different reproductive strategies.     

Potential for parthenogenesis of virgin females in a bisexual population of the geographically parthenogenetic mayfly Ephoron shigae (Insecta: Ephemeroptera,Polymitarcyidae)

The burrowing polymitarcyid mayfly Ephoron shigae is a geographically parthenogenetic species. Interestingly, the distributions of the bisexual and unisexual populations overlap broadly in their respective geographic ranges. In this mayfly, obligatory diploid thelytoky appears within unisexual populations. In the present study, we examined the potential for parthenogenesis or the parthenogenetic ability of females in a bisexual population aiming to understand the emergence of unisexual populations. The results obtained revealed that females in the examined bisexual populations showed a potential for diploid thelytoky as also seen in the unisexual populations, although, in females from bisexual populations, the development success rates of their unfertilized eggs were considerably lower than those of virgin females from unisexual populations. In the three bisexual reproducing species (Ephemera japonica, Ephemera strigata, and Ephemera orientalis) in the closely‐related family Ephemeridae, diploid thelytoky (i.e. tychoparthenogenesis; < 3%) was also observed. However, in this case, the parthenogenetic development success rates of unfertilized eggs were significantly lower than those of virgin females in the bisexual (Hino‐yosui Irrigation Canal) population of E. shigae. Accordingly, we suggest that parthenogenetic ability (i.e. tychoparthenogenesis or facultative parthenogenesis) in bisexual populations of E. shigae may facilitate the evolutionary transition to unisexual populations with fully obligatory parthenogenesis. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 326–334.     

All-female broods and mimetic polymorphism in Acraea encedon (L.) (Lepidoptera: Acraeidae) in Tanzania

In some populations of the African butterfly, Acraea encedon, there are two kinds of females, one producing offspring in a normal 1:1 sex ratio, the other producing females only; in other populations the sex ratio is apparently normal. All-female broods had hitherto been mainly associated with populations in which field sampling revealed an excess of females. The all-female brood trait is described from a population at Dar es Salaam which field sampling suggested was normal, and this indicates that the trait may be much more widespread and common than had previously been supposed. This discovery also extends the known distribution of the trait across Africa from Sierra Leone to eastern Tanzania. The butterfly is also a polymorphic Müllerian mimic of Danaus chrysippus, which is a highly unusual phenomenon as Müllerian mimicry is almost invariably monomorphic. The relative frequencies of two corresponding colour forms of the two species of butterflies at Dar es Salaam adds support to the hypothesis that they are indeed Mullerian mimics. The results of breeding experiments suggest that the polymorphic forms in Acraea encedon are allelic with dominance.     

Phylogeographic assessment of mtDNA paraphyly and the evolution of unisexuality in Calligrapha (Coleoptera: Chrysomelidae)

The leaf beetle genus Calligrapha is one of the few examples of animals with several obligate unisexual, female‐only species. Previous work showed that each one arose independently from interspecific hybridization events involving different species. However, all of them clustered in a single mtDNA clade together with some individuals of the parental bisexual species, which appeared as deeply polyphyletic in the mtDNA genealogy of the genus. The dating of these splits using a molecular clock placed them in the Quaternary and it was hypothesized that climatic change during this period may have favored range expansions and secondary contacts required for hybridization. In this work, we test this hypothesis and the origins of unisexuality in Calligrapha examining the diversity of mitochondrial (cox1) and nuclear (wingless, Wg) genes and the Bayesian continuous mtDNA phylogeography of a sample of more than 500 specimens of two bisexual species of Calligrapha at a continental scale and two unisexual species derived from them. Besides a major topological difference, whereby each bisexual species is monophyletic for Wg but paraphyletic for cox1, both gene datasets are consistent with a minimum of seven evolutionary lineages, coherent with geography and consistent with an ordered expansion to occupy their current ranges. The results also imply their survival in well‐established glacial refuges during the Last Glacial Maximum (LGM). Thus, for bisexual C. multipunctata there are two main, southern and northern lineages. The southern lineage expanded its range in two evolutionary branches, to the Rocky Mountains and to the northern Mississippi and Ohio River basins, respectively. The northern lineage has one branch in the Upper Mississippi and one that expanded west to the Pacific Northwest and east to the northeastern North Atlantic, finding refuge in both areas. These major lineages are parapatric in the Northern Great Plains, an area consistent with them having found refuge in the so‐called Driftless region during the LGM. For bisexual C. philadelphica, one northern lineage expanded west from the northern Appalachians and one east and southwest along the axis of the Appalachians, and the timing of events is consistent with their persistence in glacial refugia at both sides of the main Great Lakes lobe of the Laurentide Ice Sheet. There is evidence that the northeastern North Atlantic lineages of both species hybridized at the edge of their ranges after the LGM. The additional, divergent mtDNA lineage of these species shows evidence of range expansions of two lineages, one for each species, in an area south of the Laurentide Ice Sheet, and giving origin to the unisexual species by way of hybridization with other species in the Alleghanian region after the LGM. Interestingly, the individuals of supposedly bisexual species in this clade are all females. This suggests that unisexuality actually predates the origin of unisexual taxa in this system and that some bisexual species in Calligrapha may be species complexes instead, with cryptic species differing in their reproductive mode.     

Unisexual broods and sex ratios in a polyembryonic encyrtid parasitoid (Copidosoma sp.: Hymenoptera)

Summary We examined brood sex ratios of an undetermined species of Copidosoma. Most broods (65%) were unisexual, with a greater proportion of female broods. Some mixed broods contained extremely small proportions of wasps of the opposite sex. Our results imply that the female-biased sex rations in this species cannot be explained by local mate competition theory.     

Sex ratio in relation to timing of breeding, and laying sequence in a dimorphic seabird

When the cost of rearing sons and daughters differs and the subsequent survival and reproductive success of one sex is more dependent than the other, on the amount of parental investment, adult females tend to produce more chicks of the more dependent sex if the females are in good condition themselves. One method of varying the total investment in each sex is through modifying the sex ratio of offspring produced. This study shows that in broods of European Shags Phalacrocorax aristotelis , the sex ratio varied with laying date. Presumably in this species, the lifetime reproductive success of males is more dependent on the level of parental investment. Early breeders are in better condition, the brood sex ratio of early broods was male biased (0.63), while that of late broods was female biased (0.36). The overall difference in sex ratio found between early and late nests could be attributed to manipulation of sex in the first laid egg. In early broods, 77% of the first hatched chicks were male but only 30% of the first hatched chicks in late broods were male. The sex combination of the first two chicks in a brood significantly affected growth as measured by asymptotic mass.     

Structural heterozygosity in parthenogenetic populations of Cnemidophorus lemniscatus (Sauria,Teiidae) from the Amazonas valley

C. lemniscatus is the only species of the genus Cnemidophorus found in the Amazonas valley. Among the populations from 15 localities which were studied, 5 included individuals of both sexes, but the remaining 10 were composed only by parthenogenetic females. In every case the all-female populations presented one or more heteromorphic pairs of chromosomes; in no case did this happen in the sexual populations. Five different karyotypes were described but no two of them were present in the same locality. No triploid individuals were found. A hypothesis for explaining this situation is discussed. It is probable that the chromosomes of the ancestral sexual population presented structural balanced polymorphisms preserved by heterosis or by better adaptation of each homozygote to a different niche. The latter case explains better the finding of different karyotypes without heteromorphism in different bisexual populations. When occasional parthenogenesis happened to appear in an heterotic structural heterozygote a successful strain could be established which would displace its bisexual competitors.     

Insemination Capacity and Dispersal in Relation to Sex Allocation Decisions in Goniozus legneri (Hymenoptera: Bethylidae): Why Are There More Males in Larger Broods?

Models considering sex ratio optima under single foundress strict local mate competition predict that female bias will be reduced by stochasticity in sex allocation, developmental mortality of males and limited insemination capacity of males. In all three cases the number of males per brood is expected to increase with brood size. Sex ratio optima may also be less female biased when several mothers contribute offspring to local mating groups or if non‐local mating occurs between members of different broods; again more males are expected in larger broods. In the parasitoid wasp Goniozus legneri (Hymenoptera: Bethylidae), sex allocation has only a small stochastic component, developmental mortality is low and non‐siblings are unlikely to develop in the same brood. However, the number of males per brood increases with the size of the brood (produced by a single mother). We investigated the further possibilities of limited insemination capacity and non‐local mating using a naturalistic experimental protocol. We found that limited insemination capacity is an unlikely general explanation for the increase in number of males with brood size. All males and females dispersed from both mixed and single sex broods. Although most females in mixed sex broods mated prior to dispersal, these data suggest that non‐local mating is possible, for instance via male immigration to broods containing virgin females. This may influence sex ratio optima and account for the trend in male number.     

Reduction of competition between bisexual and unisexual females ofPoecilia in northeastern Mexico

Synopsis Breeding compexes of poeciliid fishes with a bisexual and two unisexual species were studied for mechanisms permitting Sympatric coexistence. The unisexuals are gynogenetic and thereby sexually dependent on the males of the bisexual species for sperm to initiate development, but inheritance is entirely maternal.Bisexual females are more abundant in headwater localities; unisexuals increase in downstream localities. Males were 10 – 18% of the total poeciliid population, regardless of the relative proportions of bisexual to unisexual females. Downstream localities were typified by greater habitat diversity, including a variety of backwater pools. The unisexuals showed a marked preference for such pools. Both field and laboratory studies showed that all three types of females as well as males preferred shaded areas with a gravel substrate.Although the four types of fish were found together, nearest neighbour data indicated that each type of female preferred its own kind. Males courted throughout the year and were indiscriminate in their choice of mates. Despite the skewed sex ratio, males were not in short supply because only a few females were sexually receptive at a given time. No significant differences existed between bisexuals and unisexuals in their relative reproductive outputs, but they were asynchronous.     

Reproductive behavior and the maintenance of all-female Poecilia

Synopsis There are four members involved in the breeding complexes of poeciliid fishes found in the freshwaters of northeastern Mexico: males and females of a bisexual species, and diploid and triploid unisexuals. Both unisexuals reproduce by gynogenesis, i.e., an asexual type of reproduction where the sperm triggers egg development but the male genome is excluded to produce clonal offspring. The three types of females are closely related, which suggests that they are potential competitors since all three require the service of the same males. The potential for competition is compounded by a highly skewed sex ratio in favor of females. On the average the unisexuals comprise about 30% of the Poecilia females. This high frequency coupled with a close genetic relatedness to their bisexual hosts, raises the question of how the unisexuals are maintained in nature.Other investigators who work with bisexual/unisexual complexes in the related genus, Poeciliopsis, have postulated that male dominance hierarchies are responsible for restricting the access of subordinate males to their conspecific females. Consequently, these subordinate males mate with unisexual females. The current report tests whether or not this hypothesis applies to bisexual/unisexual complexes of Poecilia.We have found that linear dominance hierarchies appear to function in the defense of home ranges and do not restrict access of males to females. Dominant males exhibit less mating activity than subordinate males towards females. Previous reports showed that males are reproductively competent throughout the year, whereas females show striking asynchrony in their reproductive readiness. Such asynchrony limits the proportion of receptive females at any one time. Consequently, there are more males ready to mate than there are females receptive to their mating attempts. This may lead to mating frenzies. We postulate that these indiscriminate matings maintain the fertility of both unisexuals. When the relative reproductive outputs of adult females are compared, both unisexuals appear as fit as their bisexual congeners.     

Cooperation, conflict, and crèching behavior in goldeneye ducks

Crèching behavior, or brood amalgamation, results in offspring being reared by adults other than their genetic parents. Although a variety of hypotheses have been proposed to explain this behavior, most assume either that brood amalgamation is accidental (i.e., nonselected) or that adoption of young is selected for because of social benefits to the young and/or adopting parents. We propose, instead, that brood amalgamation is a function of two separate processes: brood desertion and brood adoption. To examine brood desertion, we develop a graphic model to predict when parents should abandon their young and we test this model experimentally for the Barrow's goldeneye (Bucephala islandica). As predicted, females deserted their offspring when the size of the brood was experimentally reduced. Brood adoption occurred when deserted ducklings joined other broods. However, the success of ducklings in doing so was strongly dependent on the availability of potential host broods and on the age of the recipient broods. Foreign ducklings were readily accepted into young broods (<10 d old) but invariably were rejected from old broods. We could detect no benefits or costs of brood adoption to the host females, contrary to the expectations of a social benefit hypothesis. Our experiments indicate that Crèching behavior is driven by selection on adults to abandon their brood when the benefits of continued investment are outweighed by the reduction in future reproduction and selection on deserted ducklings to join other broods to obtain parental care. Rather than a form of cooperative brood care, Crèching in goldeneyes is perhaps best considered as a form of reproductive parasitism, entailing parent-offspring conflict over brood desertion and intergenerational conflict over adoption of abandoned young.     

木薯两性花及其种子的形态特征

以前期发明的一种木薯(Manihot esculenta)调控开花技术为基础, 成功研发出木薯两性花诱导技术, 并发现诱导出的木薯两性花能自花授粉结实。该文报道了木薯两性花、两性花自花授粉发育的蒴果及其种子的形态特征。木薯两性花同时具有雌蕊和雄蕊, 而单性花只具有雌蕊或雄蕊; 两性花蒴果卵圆形且长宽比大, 单性花蒴果阔椭圆形且长宽比小; 两性花种子种脊不隆起, 单性花种子种脊隆起明显。两性花和两性花种子是珍贵的木薯育种材料, 对揭示木薯的遗传特性及培育木薯新种质具有重要意义。