Moms are better nurses than dads: gender biased self‐facilitation in a dioecious Juniperus tree

Questions: Can gender of nurse plants affect regeneration patterns and spatial population structure? Is there a seed‐seedling conflict in the regeneration process? What factors are responsible for the clumped spatial population structure observed for adult trees? Location: Mediterranean cold semi‐arid high mountains in Spain. Methods: The spatial pattern of adult Juniperus thurifera trees was studied by means of Ripley's K‐analysis. χ² analyses were used to test for natural seedling frequency in each of three main microhabitats: (1) under female and (2) male tree canopies and (3) in open interspaces. The observed pattern was explained experimentally by studying seed and seedling survival for two years. Survival probabilities were calculated across life stages for each of three main microhabitats. Results: Adult J. thurifera trees were aggregated in space. Most seedlings were found underneath female J. thurifera trees. Experimental studies demonstrated that from seed dispersal to seedling survival all life stages showed the same positive or negative trend within a given microhabitat, indicating stage coupling and no seed‐seedling conflicts. Attraction of frugivo‐rous birds by reproductive female junipers and improvement of environmental conditions beneath tree canopies were the main factors responsible for the variation in seedling density among microhabitats; highest underneath female trees and lowest in open interspaces. Conclusions: In dioecious species, the gender of nurse plants can significantly determine the spatial population structure. In J. thurifera forests, facilitation beneath female trees occurs among all life stages without any sign of seed‐seedling conflict. The most critical factors shaping the spatial population structure were directed seed dispersal and environmental amelioration beneath female conspecific trees.     

Differential niche modification by males and females of a dioecious herb: extending the Jack Sprat effect

Males and females of dioecious plants often differ in morphological, physiological and life‐history traits, probably as a result of their different requirements for reproduction. We found that the growth and reproductive effort of individuals of the dioecious herb Mercurialis annua depended on whether males or females had been growing in the soil previously. This suggests that males and females of M. annua differentially modify the soil in which they are growing. Our study indicates that sexual dimorphism in dioecious plants can give rise to increased environmental heterogeneity as a consequence of sex‐specific niche modification.     

Sexual dimorphism in a dioecious population of the wind-pollinated herb Mercurialis annua: the interactive effects of resource availability and competition

Background and Aims

Male-biased sex allocation commonly occurs in wind-pollinated hermaphroditic plants, and is often positively associated with size, notably in terms of height. Currently, it is not well established whether a corresponding pattern holds for dioecious plants: do males of wind-pollinated species exhibit greater reproductive allocation than females? Here, sexual dimorphism is investigated in terms of life history trade-offs in a dioecious population of the wind-pollinated ruderal herb Mercurialis annua.

Methods

The allocation strategies of males and females grown under different soil nutrient availability and competitive (i.e. no, male or female competitor) regimes were compared.

Key Results

Male reproductive allocation increased disproportionately with biomass, and was greater than that of females when grown in rich soils. Sexual morphs differentially adjusted their reproductive allocation in response to local environmental conditions. In particular, males reduced their reproductive allocation in poor soils, whereas females increased theirs, especially when competing with another female rather than growing alone. Finally, males displayed smaller above-ground vegetative sizes than females, but neither nutrient availability nor competition had a strong independent effect on relative size disparities between the sexes.

Conclusions

Selection appears to favour plasticity in reproductive allocation in dioecious M. annua, thereby maintaining a relatively constant size hierarchy between sexual morphs. In common with other dioecious species, there seems to be little divergence in the niches occupied by males and females of M. annua.     

Epiphytic bryophytes in harsh environments: the Juniperus thurifera forests

Abstract

The forests of Juniperus thurifera are peculiar ecosystems that typically grow on mountains and highplateaux of the western Mediterranean basin with dry and continental climates. Some previous surveys suggested that these forests house a rather distinctive epiphytic bryophyte flora. Epiphytic bryophyte communities were systematically sampled in 19 representative juniper forests, for the first time spanning all the distribution area of this conifer. The flora consists of 44 species (32 acrocarpous mosses, 10 pleurocarpous mosses and 2 liverworts). Orthotrichum species are the most frequent and abundant in most of the sampled localities, including some uncommon taxa such as Orthotrichum vittii which shows a clear association with J. thurifera. Epiphytic bryophyte communities on this species were highly homogeneous, although they can be arranged into different groups in response to environmental conditions. Typically, the epiphytic communities of the Mediterranean juniper forests comprise a distinct combination of xerophytic taxa that enhances the interest of these ecosystems and provides new fields for their research and conservation.     

Sex ratio and sexual dimorphism in mountain dioecious thuriferous juniper (Juniperus thurifera L., Cupressaceae)

Thuriferous juniper ( Juniperus thurifera L), a dioecious bush or tree is only found in isolated parts of the western Mediterranean: France, Spain, Algeria and Morocco. These mountain juniper stands are seriously endangered in Morocco as a result of intensive wood removal, and in Europe as a result of recolonization of stands by pines or oaks. Field studies were conducted to investigate sex ratio and sexual dimorphism, never previously examined, in eight different populations in the Atlas mountains and, for comparison, in one of two populations in the French Pyrenees. The sex ratio was female-biased for six of the eight Moroccan stands and especially for the oldest populations. The Pyrenean population showed a similar female-biased ratio. This particular sex ratio is possibly linked to cost of reproduction, paid by both males and females. Sex ratios can also be linked to population dynamics. Males begin to flower slightly younger than females, which explains their apparent dominance in young populations in Morocco or in a recolonization zone with young trees in the Pyrenees. Studies concerning sexual dimorphism in the western High Atlas sites showed no significant difference in phytomass between males and females. Females appear to be significantly taller but with a lower radial growth. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 138 , 237–244.     

Allocation to floral structures in Thalictrum pubescens (Ranunculaceae), a cryptically dioecious species

Females of Thalictrum pubescens produce stamens that contain sterile pollen, whereas males are both functionally and morphologically unisexual. This study examines the investment in stamen production by females of T. pubescens by comparing the female structures with those of their fully functional male counterparts. Stamens from females had the same biomass and contained the same amount of nitrogen and phosphorus as stamens from males. Anther size was the same in males and females, but filaments were longer in stamens from males. Females produced more pollen per anther than males, and pollen size was the same in both sexes. Within flowers, there was a positive correlation between the amount of pollen per anther and the length of anthers in males, but not in females. This would be expected if males growing in better environmental conditions or with greater vigour invested more resources in pollen production, thereby increasing fitness. Females, who receive no fitness benefits from increased pollen production, did not show this pattern. There was also evidence of a trade-off within female flowers between the number of stamens and the number of pistils. This trade-off was noted in conditions when variance among plants was reduced, namely in the field during a year when flower size was particularly small and in a previous glasshouse study. Therefore, it appears that when environmental variance is low, stamens are produced at the expense of producing more pistils, and hence seeds. In conclusion, stamen production does not appear to be inconsequential to females of Thalictrum pubescens.     

Resource allocation during ontogeny is influenced by genetic,developmental and ecological factors in the horned beetle,Onthophagus taurus

Resource allocation trade-offs arise when developing organs are in competition for a limited pool of resources to sustain growth and differentiation. Such competition may constrain the maximal size to which structures can grow and may force a situation in which the evolutionary elaboration of one structure may only be possible at the expense of another. However, recent studies have called into question both the consistency and evolutionary importance of resource allocation trade-offs. This study focuses on a well-described trade-off between the horns and eyes of Onthophagus beetles and assesses the degree to which it is influenced by genetic, developmental and ecological conditions. Contrary to expectations, we observed that trade-off signatures (i) were mostly absent within natural populations, (ii) mostly failed to match naturally evolved divergences in horn investment among populations, (iii) were subject to differential changes in F₁ populations derived from divergent field populations and (iv) remained largely unaffected by developmental genetic manipulations of horn investment. Collectively, our results demonstrate that populations subject to different ecological conditions exhibit different patterns of, and differential plasticity in, resource allocation. Further, variation in ecological conditions, rather than canalized developmental mechanisms, may determine whether and to what degree morphological structures engage in resource allocation trade-offs.     

Past,present, and future geographic range of the relict Mediterranean and Macaronesian Juniperus phoenicea complex

AimThe aim of this study is to model the past, current, and future distribution of J. phoenicea s.s., J. turbinata, and J. canariensis, based on bioclimatic variables using a maximum entropy model (Maxent) in the Mediterranean and Macaronesian regions.LocationMediterranean and Macaronesian.TaxonCupressaceae, Juniperus.MethodsData on the occurrence of the J. phoenicea complex were obtained from the Global Biodiversity Information Facility (GBIF.org), the literature, herbaria, and the authors’ field notes. Bioclimatic variables were obtained from the WorldClim database and Paleoclim. The climate data related to species localities were used for predictions of niches by implementation of Maxent, and the model was evaluated with ENMeval.ResultsThe potential niches of Juniperus phoenicea during the Last Interglacial period (LIG), Last Glacial Maximum climate (LGM), and Mid‐Holocene (MH) covered 30%, 10%, and almost 100%, respectively, of the current potential niche. Climate warming may reduce potential niches by 30% in RCP2.6 and by 90% in RCP8.5. The potential niches of Juniperus turbinata had a broad circum‐Mediterranean and Canarian distribution during the LIG and the MH; its distribution extended during the LGM when it was found in more areas than at present. The predicted warming in scenarios RCP2.6 and RCP8.5 could reduce the current potential niche by 30% and 50%, respectively. The model did not find suitable niches for J. canariensis during the LIG and the LGM, but during the MH its potential niche was 30% larger than at present. The climate warming scenario RCP2.6 indicates a reduction in the potential niche by 30%, while RCP8.5 so indicates a reduction of almost 60%.Main conclusionsThis research can provide information for increasing the protection of the juniper forest and for counteracting the phenomenon of local extinctions caused by anthropic pressure and climate changes.     

Gender-specific costs of reproduction on vegetative growth and physiological performance in the dioecious shrub Corema album

Background and Aims

Reproductive costs imply trade-offs in resource distribution at the physiological level, expressed as changes in future growth and/or reproduction. In dioecious species, females generally endure higher reproductive effort, although this is not necessarily expressed through higher somatic costs, as compensatory mechanisms may foster resource uptake during reproduction.

Methods

To assess effects of reproductive allocation on vegetative growth and physiological response in terms of costs and compensation mechanisms, a manipulative experiment of inflorescence bud removal was carried out in the sexually dimorphic species Corema album. Over two consecutive growing seasons, vegetative growth patterns, water status and photochemical efficiency were measured to evaluate gender-related differences.

Key Results

Suppression of reproductive allocation resulted in a direct reduction in somatic costs of reproduction, expressed through changes in growth variables and plant physiological status. Inflorescence bud removal was related to an increase in shoot elongation and water potential in male and female plants. The response to inflorescence bud removal showed gender-related differences that were related to the moment of maximum reproductive effort in each sexual form: flowering in males and fruiting in females. Delayed costs of reproduction were found in both water status and growth variables, showing gender-related differences in resource storage and use.

Conclusions

Results are consistent with the existence of a trade-off between reproductive and vegetative biomass, indicating that reproduction and growth depend on the same resource pool. Gender-related morphological and physiological differences arise as a response to different reproductive resource requirements. Delayed somatic costs provide evidence of gender-related differences in resource allocation and storage. Adaptive differences between genders in C. album may arise through the development of mechanisms which compensate for the cost of reproduction.     

小五台山青杨雌雄植株树轮生长特性及其对气候变化的响应差异

近年来逆境导致植物雌雄幼苗的生长出现差异被许多控制实验所证实, 而有关气候变化对雌雄异株植物成树生长的潜在影响尚未引起人们广泛的关注。为进一步揭示气候变化对雌雄植株树木径向和密度生长的不同影响, 该文通过树轮生态学的研究方法, 选择小五台山天然青杨(Populus cathayana)种群为研究对象, 对青杨雌雄植株近30年(1982-2011)的树轮生长特性及其与气候的相关性进行了分析。结果显示: 1)在近30年当地气温不断升高的气候条件下, 雌株的年轮最大密度和晚材平均密度均高于雄株(p < 0.05), 但雌雄植株的径向生长无显著差异; 2)雌雄植株年轮最大密度和宽度差值年表的变化趋势具有一致性, 但在年轮最大密度差值年表的变化上雄株波动幅度大于雌株; 3)青杨雌雄植株年轮密度差值年表对温度响应的月份明显不同。雌株年轮最大密度与当年8月的月平均最高气温显著正相关, 而雄株年轮最大密度与当年1月和4月的气温负相关; 4)生长季前的气候变化对青杨雌雄植株的径向生长均有明显的限制作用。此外, 当年6月的高温对于早材生长的限制作用特别明显。上述结果表明, 雌雄异株植物在树木年轮生长方面对全球气候变暖可能具有不同的响应机制, 雌株比雄株更侧重于密度生长。     

Gender-specific characteristics of tree-ring growth and differential responses to climate change in the dioecious tree Populus cathayana in Xiaowutai Mountains,China

近年来逆境导致植物雌雄幼苗的生长出现差异被许多控制实验所证实, 而有关气候变化对雌雄异株植物成树生长的潜在影响尚未引起人们广泛的关注。为进一步揭示气候变化对雌雄植株树木径向和密度生长的不同影响, 该文通过树轮生态学的研究方法, 选择小五台山天然青杨(Populus cathayana)种群为研究对象, 对青杨雌雄植株近30年(1982-2011)的树轮生长特性及其与气候的相关性进行了分析。结果显示: 1)在近30年当地气温不断升高的气候条件下, 雌株的年轮最大密度和晚材平均密度均高于雄株(p < 0.05), 但雌雄植株的径向生长无显著差异; 2)雌雄植株年轮最大密度和宽度差值年表的变化趋势具有一致性, 但在年轮最大密度差值年表的变化上雄株波动幅度大于雌株; 3)青杨雌雄植株年轮密度差值年表对温度响应的月份明显不同。雌株年轮最大密度与当年8月的月平均最高气温显著正相关, 而雄株年轮最大密度与当年1月和4月的气温负相关; 4)生长季前的气候变化对青杨雌雄植株的径向生长均有明显的限制作用。此外, 当年6月的高温对于早材生长的限制作用特别明显。上述结果表明, 雌雄异株植物在树木年轮生长方面对全球气候变暖可能具有不同的响应机制, 雌株比雄株更侧重于密度生长。     

Sexual dimorphism in intra- and interspecific competitive ability of the dioecious herb Mercurialis annua

Males and females of dioecious plant species often show different responses to competition with individuals of the same or opposite gender, but almost no data are available on the outcome of competition with members of other species. Here, we show that male and female individuals of the wind-pollinated herb Mercurialis annua are sexually dimorphic in both their intraspecific and interspecific competitive abilities. In a controlled experiment, we found that both sexes of M. annua were negatively affected by interspecific competition, but the sensitivity of males and females depended on the identity of their competitor species, with females tending to suppress the aboveground growth of competitor species more than males. Further, we found that intrasexual and intersexual competition affected the aboveground growth of males but not that of females: only males showed a significant reduction in growth when growing with conspecific competitors (male or female). We discuss our results with reference to related studies that suggest that males and females of M. annua have different resource requirements for reproduction, which in turn affect their competitive abilities.     

Sex ratios, size distributions, and sexual dimorphism in the dioecious tree Ilex aquifolium (Aquifoliaceae)

Sex ratio and sexual dimorphism in physiology and growth were studied in the dioecious tree Ilex aquifolium at two localities in northern Spain. Genet sex ratio was significantly male biased in one locality but not in the other. However, ramet and flowering ramet sex ratios were male biased at both study sites. Males had significantly thicker main trunks than females in one locality and produced more ramets in the other. Growth rate, estimated from mean width of annual rings, did not differ between localities, but males produced wider rings than females at both sites. Mean annual growth rates over the last 10, 20, and 30 yr were significantly higher for males. Measurements of chlorophyll fluorescence indicated that the efficiency of photosynthesis of leaves on nonfruiting branches of females was higher than for leaves on branches of male plants under low-light conditions, though not under saturating-light conditions. Efficiency of photosynthesis was significantly lower on fruiting branches of female plants than on nonfruiting branches. We discuss whether the observed between-sex differences are attributable to the higher cost of reproduction in females and/or to pollen competition.     

Sex ratio and reproductive effort in the dioecious Juniperus communis subsp. alpina (Suter) Celak. (Cupressaceae) along an altitudinal gradient

The hypothesis that reproductive cost differs between sexes was tested in Juniperus communis subsp. alpina along an altitudinal gradient. Sex ratio (male : female) increased significantly with elevation, and above 2,600 m it was significantly male-biased. The reproductive effort was markedly greater for females than for males at all elevations. However, over 3 years of study, the growth of the females, measured as elongation of the main axes, was similar to that of the males. In both sexes, growth decreased with increasing elevation. Neither size of the ripe seed cones, nor the number of developed seeds per cone varied with elevation. The percentage of filled seeds was significantly greater at higher elevations indicating more favourable conditions for wind pollination in these stands. However, cone production decreased with elevation and so, reproductive success of J. communis subsp. alpina in Sierra Nevada decreases towards both upper and lower altitudinal distribution limits. The results do not support the hypothesis of differential reproductive cost between sexes; thus, alternative arguments to explain the altitudinal variation of sex ratio are discussed.     

Breeding biology, resource partitioning and reproductive effort of a dioecious shrub, Clutia pulchella L. (Euphorbiaceae)

 The flowering of Clutia pulchella was studied in a coastal scarp forest community in southern KwaZulu-Natal, South Africa. Sex dependent differences in the frequency and magnitude of floral output were recorded, with male individuals producing 4.32 times more flowers per leaf axis than females. Increased node production, as a manifestation of significantly increased branching, allowed for prolific flower production in males. Energy investment per flower was marginally greater in females (0.045 J/mg), despite copious pollen production and glandular secretion in males (0.035 J/mg). Differential flower production, reproductive organ dry mass and an unbalanced branching ratio revealed that “per plant” expenditure towards flowering was more pronounced in males (♀ flowering × 5.04). The elevated cost of fruit production (♀ flowering × 5.5), inclusive of imperfect fruit set, resulted in overall reproductive expense being slightly higher for females. Such sex-dependent reproductive investment was shown to have minimal influence on the population sex ratio, with sex frequencies and nearest neighbor distances yielding a non-significant male bias of 1.16. No evidence of spatial asymmetry was found. Received December 1, 1999 Accepted September 27, 2000     

In the lack of extreme pioneers: trait relationships and ecological strategies of 66 subtropical tree species

Aims Despite the growing interest in the topic of functional ecology, there are still forest regions that have not been examined, as most work has been done in the tropics. Unresolved issues include the strength of a growth-mortality trade-off in trees (originally identified for seedlings) and the nature of the association between plant traits and vital rates, if any. Our objectives were to examine whether (i) ecological strategies in South American mixed forests are organized along the fast competitor × slow stress-tolerator and height gradients as the main strategy axes depicted in the overall trait and vital rate correlation structure, and (ii) a tentative path model we proposed can explain the patterns of covariation among traits and vital rates.Methods We studied a different habitat (subtropical mixed conifer-hardwood forests) and region (Brazilian Atlantic Forest) from the majority of related studies in forests, carried out in the Neotropical region. Data on total height, stem slenderness, crown depth, wood density, specific leaf area, leaf and seed length, seed dispersal mode, annual mortality, diameter relative growth rate and relative growth rate under favorable conditions were measured in southern Brazil for 66 tree species. Data were subjected to principal components analysis and path analysis. Restricted data on saplings and treelets were analyzed through correlation.Important findings Studied traits were reduced to four principal components. Principal components analysis produced axes that fit the resource acquisition versus resource-conservation and the height-mortality trade-offs, although the former was split into two distinct axes. Seed size and seed dispersal mode appeared independently of these axes. A path model showed that leaf length and specific leaf area caused direct changes in trunk slenderness and, indirectly through growth, affected mortality. Expected trade-offs between growth and survivorship and between wood density and stem slenderness trade-offs were not found. This may result from the lack of extreme pioneers and over-representation of slow-growing hardwood species found in Atlantic subtropical forests of South America. This suggests that the fastest growing species in the region do not grow so fast as to compromise wood density and survivorship, but grow fast enough to benefit from increased size. Relationships between traits and vital rates seem to be mediated by the assembly process of regional floras, and the relative importance of traits like SLA and wood density may vary between floristic regions.