Low Reproductive Success in Two Subspecies of Juniperus Oxycedrus L

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Int. J. Plant Sci. 159(5):843-847. 1998. (C 1998 by The Universityof Chicago. All rightsreserved. 1058-5893/98/5905-0020$03.00

LOWREPRODUCTIVE SUCCESS IN TWO SUBSPECIES OF JUNIPERUS OXYCEDRUS L.

Pedro L. Ortiz,' Montserrat Arista, and Salvador Talavera Departamentode Biologia Vegetal y Ecologia, Universidadde Sevilla, Apdo. 1095, 41080 Sevilla, Spain

Mature seed cone and seed productionwere studied in six populationsof Juniperusoxycedrus (three of subspecies oxycedrusand threeof subspecies macrocarpa). In both subspecies, seed cone abortiontook place mainlyjust after the pollination period, and most of the remaining seed cones reached full size. Percentage of mature cones was significantlyhigher in subspecies oxycedrusthan in macrocarpa. In bothtaxa, seed cones developed fullyin the absence of filledseeds. Both the numberof full-sizedseeds per cone and the seed viabilitywere low, and theywere similarin both subspecies. However, seed potentialwas markedlyhigher in subsp. macrocarpa (mean 4.1 ovules/cone)than in subspecies oxycedrus(mean 2.8 ovules/cone),indicating a lower seed efficiencyin subspecies macrocarpa. Results indicate thatdeficient pollination and site quality can be causes of low seed cone productionand low seed viabilityin both subspecies of J. oxycedrus. Introduction grow on mountainousand on sandy coastal zones, respectively.Both subspecies of J. oxycedrusare shrubs-or some- One of the most common ecological problems in times small trees-that have a 2-yrreproductive cycle. Pol- conifersis the reductionin viable seed crops (Colan- lination occurs in October-November in a given year, geli and Owens 1990; Owens et al. 1990; Arista and fertilizationtakes place in May-June of the followingyear, Talavera 1996). Lack of pollination,low pollen via- and seed cones are ripe in September-Octoberof the second bility,or embryo degeneration(as a consequence of year (M. Arista et al., unpublisheddata). Ripe seed cones selfing)have all been implicatedas causes of reduced are axillary,dark red, fleshy,and globose and are bigger in seed production(Owens et al. 1991; Arista and Tala- subspecies macrocarpa (about 16 mm vs. 10 mm in subsp. oxycedrus). vera 1996). Among conifers,monoecy is the predom- The studywas carriedout from 1994 to 1996 in six pop- inant breeding system; the presence of male and fe- ulationsof J. oxycedrus:three of subsp. oxycedrusand three male structuresin the same plant often leads to of subsp. macrocarpa (table 1). During October-November, self-pollinationand consequentlyendogamy. However, the sexual ratio (number of male plants/numberof female in some monoecious conifersthe spatial separationof plants) was determinedin each population. Production of female and male structures(Kuittinen and Savolainen seed cones was studied using five to six randomlyselected 1992), the temporaldifference between receptivityof branchesper plant on ca. 10 individualsin each population. female cones and sheddingof pollen in the same plant These brancheswere markedand theirseed cone production, (dichogamy,Sarvas 1962), or a subdioecious condition the numberof seed cones in developmentafter pollination, (Jordano1991; Wilson et al. 1996; Aristaand Talavera and the number of seed cones that ripened were counted. Mature seed cones were collected in Octoberjust beforedis- 1997) reduce the rate of selfing. persion and the total number of full-sized seeds per cone One of the most effectivealternatives for preventing was determined.Flat seeds were not counted.Each full-sized inbreedingis dioecy; however,because male and fe- seed (hereafter,called simply "seed") was cut lengthwiseto male strobiliare on separate trees,dioecy can lead to determineembryo presence (seeds withembryo are denoted a lack of pollination.Among conifers,dioecy is a rare as "filled seeds," and those withoutit are denotedas "empty breeding system,with only a few genera, e.g., Juni- seeds"). These data were used to estimatethe percentageof perus and Taxus, having dioecious species. Juniperus seed viabilityper plant and per population. is the second largest genus of the conifers,with ca. Data were analyzed using one-factorfactorial design anal- 75-80 taxa (Franco 1964). Juniperusoxycedrus L. is yses of variance (ANOVA). When significantdifferences be- < these were a dioecious species widely distributedin the Mediter- tween populations were presented (P 0.05), located with Tukey tests. Prior to any statisticalanalyses, ranean region (Franco 1964). There is littleinforma- variables were checked for normalityand transformedas tion about seed crops in dioecious junipers (Houle and necessary. Deviation fromunity for the sex ratio of the six Babeux 1994), and no data about cone or seed pro- populations was verifiedwith the G test (Sokal and Rohlf ductionare available forJ. oxycedrus.The aim of this 1981). study was to determineinterpopulation and intersub- species variationsin matureseed cone and seed pro- Results ductionin J. oxycedrus. Interplant and Interpopulation Variation Materialand Methods Cone abortion was absent or rare during postpolli- Juniperusoxycedrus has two common subspecies in nation developmental in all populations. Percentage of southwesternSpain, J. oxycedrussubspecies oxycedrus and mature cones was markedly variable between plants J. oxycedrussubsp. macrocarpa (Sibth. & Sm.) Ball, which within each population and between populations (table 2). The Punta Umbria population had the lowest per- 'Authorfor correspondenceand reprints. centage of cone maturation (19.23%) and that of Puer- Manuscriptreceived July1997; revised manuscriptreceived March to Saucillo had the highest (43.9%; table 2). 1998. No external differences were observed between

843 This content downloaded from 128.252.067.066 on July 26, 2016 03:39:00 AM All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c). 844 INTERNATIONAL JOURNAL OF PLANT SCIENCES

Table1 Characteristicsof the Six Studied Populations of Juniperusoxycedrus in SouthernSpain Subspecies and site Province Protectionlevel Elevation Soils Situation macrocarpa: Punta Umbria...... Huelva Nature site (Enebrales de Punta Umbria) 0 m Coastal sandy Dunes beside sea Pinar de Barbate .... Cadiz Nature park (Acantilado y Pinar de Barbate) 100 m Coastal sandy Plain on sea cliff Punta Paloma ... Cadiz Unprotected 0 m Coastal sandy Dunes beside sea oxycedrus: Puerto Saucillo ...... Mdlaga Nature park (Sierra de las Nieves) 1300 m Calcareous Small valley Puerto del Boyar .... Cadiz Nature park (Sierra de Grazalema) 1100 m Calcareous Rocky slope facing south Sierra de Zafalgar ... Cadiz Nature reserve (Sierra de Grazalema) 900 m Calcareous Small valley filled and empty seeds. Filled seeds per cone ranged not significantlydifferent in the two subspecies (means fromzero to three,the modal value of the distribution of 2.3 and 1.97 in subsp. macrocarpa and subsp. ox- being zero in every population except Punta Paloma, ycedrus,respectively). Likewise, the mean numberof where it was unity(fig. 1). The mean numberof filled filledseeds per cone was similaramong subspecies, so seeds per cone varied between populations. That of that the percentageof seed viabilitywas also similar Puerto del Boyar had the lowest value (0.33; table 2) (table 3). In subspecies macrocarpa, about 47% of ma- and presented,at most, one filled seed per cone (fig. turecones had zero filledseeds, and in subspecies ox- 1). In contrast,the Punta Paloma populationpresented ycedrusthis proportion reached 56% (fig.2). The seed- the highest mean number of filled seeds per cone set (ovules that develop into filled seeds) was higher (1.11; table 2). in subspecies oxycedrus(with 21.7%) than in macro- Plants of each studied population displayed wide carpa (17.4%). differencesin seed viability.Thus, in Puertodel Boyar The presenceof two embryoswithin one seed (poly- one individual had 0% seed viability while another embryony)was found on two occasions: the firstin reached 60%. Among populations,the highestseed vi- subsp. oxycedrus(Sierra de Zafalgar population) and abilitywas foundin Punta Paloma (mean 52.58%) and the second in subsp. macrocarpa (Punta Paloma pop- the lowest were those of Puerto del Boyar and Punta ulation). Umbria (20.24% and 20.26%, respectively;table 2). The proportionsof male and female individualsdid Discussion not differfrom unity (P > 0.05) except in the Punta Mature cone productionin Juniperusoxycedrus de- Umbria population,which had a very low proportion pends on the numberof cones that develop afterpol- of male individuals (M/F = 0.4, P < 0.05; table 2). lination.Because the timebetween pollination and fer- Cone productionwas independentof sex ratio (R = tilizationis long, in this case ca. 6-7 mo (M. Arista 0.3, P = 0.55, n = 6) as were mean numberof filled et al., unpublished data), cone developmentis inde- seed per cone (R = 0.248, P = 0.635, n = 6) and pendent of ovule fertilization.In J. oxycedrus,polli- mean seed viability(R = 0.32, P = 0.536, n = 6). nation takes place in October-November.Seed cones are receptiveduring the whole pollinationperiod, but IntersubspeciesVariation unpollinated seed cones continue secreting pollen In Juniperusoxycedrus subspecies, the average per- drops for several weeks, and receptivitymay extend centage of matureseed cones was significantlyhigher even until February.The bulk of seed cone abortion in the subsp. oxycedrus(F = 9.04, P < 0.01; table 3), in this species took place duringthis stage, indicating while the numberof ovules per cone was significantly thatpollen is essential for seed cone development,as higherin subsp. macrocarpa than in the subsp. oxy- occurs in other conifers (Sarvas 1962; Dogra 1967; cedrus (F = 16.96, P = 0.0001, 1 df; table 3). Nev- Owens and Blake 1984; Colangeli and Owens 1990). ertheless,the numberof seeds in a maturecone was Thus, the percentageof maturecones reflectsthe de-

Table2 Mature Cone Production(%) and Seed Charactersof Six Populations of Juniperusoxycedrus Mature cone production(%) Filled seeds Seed viability(%) Subspecies andSe Sex population Mean + SE Range n Mean + SE Range n Mean + SE Range n ratio macrocarpa: Punta Umbria ...... 19.23 + 4.14a 1.7-48.8 14 0.60 + 0.09a 0.2-1.4 13 20.26 + 2.91a 8-45.3 13 0.4 Pinar de Barbate ... 29.39 + 4.78ab 0.7-46.6 10 0.45 + 0.IIa 0.1-1.3 10 28.99 + 6.41ab 5.9-60 10 1.16 Punta Paloma ...... 38.32 + 4.01ab 29.8-49.1 4 1.11 ? 0.13b 0.1-1.5 10 52.58 ? 6.46b 6.4-72.2 10 1 oxycedrus: Puerto Saucillo ..... 43.9 + 5.64b 15.5-71.4 13 0.74 + 0.17ab 0.05-1.6 8 40.74 + 6.96ab 2-66.6 8 1.08 Puerto del Boyar ... 28.69 + 3.45ab 7.9-39.6 10 0.33 + 0.13a 0-1 7 20.24 + 7.83a 0-60 7 1.3 Sierra de Zafalgar .. 39.86 + 3.72b 26.7-64 10 0.73 + 0.21ab 0.05-1.9 7 29.99 1 7.79ab 2.4-70.3 7 0.65

Note. Entriessharing the same superscriptdo not differsignificantly (Tukey test,P < 0.01). Range refersto mean values per plant.

60 | oxycedrus Sierra de Zafalgar Punta Umbria 50 C0 macrocarpa 100 f 100 m40 403 * 80 - 80 - 20 60 -60- 100 40 - 40- 0. 20 - 20 10 0 I0 0 1 2 3 0 1 2 3 0 1 2 3 4 Filledseedsicone Filledseeds/cone Filledseeds per cone

PuertoSaucillo Pinarde Barbate Fig.2 Frequency distributionof the numberof filled seeds per cone in Juniperusoxycedrus subsp. oxycedrusand in J. oxycedrus 100 100 subsp. macrocarpa. *,80 _ 80 ~60 60 be the main cause of this abortionrate. However, the 420 40 population of Puerto del Boyar presentedthe second ~20 20 highestrate of seed cone abortionand the highestsex 0 _j 0 ratio (M/F = 1.3). This population was situatedon a 0 1 2 3 0 1 2 3 calcareous rockyslope facing south,a site where sum- Filledseeds/cone Filledseeds/cone mer droughtwas severe. In xeric sites,the greatercost associated with the productionof fruitsas opposed to Puerto del Boyar Punta Paloma pollen can give rise to a male-biased sex ratio in di- 100 100 oecious species (Freeman et al. 1976; Willson 1979). 80 80- Moreover,in this populationmale and female individuals were clearly segregatedby niches. Female indi- 60 60- viduals were distributedalong a temporalwatercourse 40 40 that was probably the most favorable microsite.This 20 20 kind of spatial segregationof sexes is common in di- 0 0 oecious wind-pollinated species (Bierzchudek and 0 1 2 3 0 1 2 3 Eckart 1993; Freeman et al. 1997). In this situation, Filledseeds/cone Filled seeds/cone females could be pollen-limitedin the more favorable microhabitats that they dominate (Freeman et al. Fig.I Frequency distributionof the numberof filled seeds per 1993). This could be the reason of the low percentage cone in six populationsof Juniperusoxycedrus. of matureseed cones found in Puerto del Boyar population. Thus, spatial location of mates could be more gree of pollination and differsmarkedly among indi- importantthan sex ratio,if the latteris not extremely viduals. In fact, pollen dispersal in wind-pollinated low. species is highlyleptokurtic (Farris and Mitton 1984; In J. oxycedrus,the numberof seeds per cone re- Proctor et al. 1996); consequently,in dioecious spe- flectsthe numberof pollinatedovules (M. Aristaet al., cies, large variances in reproductivesuccess could re- unpublisheddata). It is remarkablethat the numberof sult fromproximity of mates (Freeman et al. 1997). ovules per cone in J. oxycedrus,although different be- The proportionof abortedseed cones was quite high tween subspecies, is lower thanthose in otherCupres- in all of the populations. The highestrate was found saceae (Owens et al. 1990; Briand et al. 1992) and in in Punta Umbria, where ca. 80% of seed cones abort- most conifers.With only two to eightovules, cones of ed. This was the only populationin which the sex ratio J. oxycedruswould need only a few pollen grains to differedsignificantly from unity. The low proportion transformall their ovules into seeds. However, only of male individuals,and consequentlyof pollen, could some of these ovules were transformedinto seeds, in-

Table3 Charactersof the Two Subspecies of Juniperusoxycedrus macrocarpa oxycedrus Character Mean ? SE Range n Mean + SE Range n Mature cone production(%) ..... 25.59 ? 2.98a 0.7-49.1 28 38.07 + 2.86b 7.9-71.4 33 Ovules/cone ...... 4.1 ? 0.25a 3-8 30 2.8 ? 0.12b 2-4 30 Seeds/cone ...... 2.31 + 0.12a 1.0-3.3 33 1.97 + 0.12a 1-2.8 22 Filled seeds/cone ...... 0.71 + 0.08a 0.1-1.5 33 0.61 ? 0.la 0-1.9 22 Seed viability(%) ...... 32.7 + 3.75a 5.9-72.2 33 30.8 + 4.51a 0-70.3 22

Note. Range refersto mean values per plant. Entriessharing the same superscriptdo not differsignificantly (ANOVA, P < 0.01).

This content downloaded from 128.252.067.066 on July 26, 2016 03:39:00 AM All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c). 846 INTERNATIONAL JOURNAL OF PLANT SCIENCES dicating a deficientpollination. Pollination problems quire an investmentof considerable magnitude for are usual in conifers(Owens and Molder 1977, 1979; reproduction.In consequence, if resourcesare limited, Singh and Owens 1981; Colangeli and Owens 1990, abortionof developing embryos is likely to occur in 1991; Arista and Talavera 1994). Deficientpollination J. oxycedrus.Decrease in reproductivefemale success is more criticalin the subspecies macrocarpa, because in xeric sites has been reportedpreviously (Freeman the two subspecies had a similarnumber of seeds per and Vitale 1985), and xeric conditionsare usual in the cone, but cones in subspecies macrocarpa had a higher Mediterraneanregion where J. oxycedrusis distribut- numberof ovules. ed. Of the seeds produced by J. oxycedrus,only ca. On the other hand, the distributionarea of J. oxy- 31 % had an embryo,leading to a similarmean number cedrus subsp. macrocarpa in southwesternSpain has of 0.6 and 0.7 filledseeds per cone in subsp. oxycedrus decreased recentlyas the consequence of urbanistic and macrocarpa, respectively.In the dioecious Juni- pressureson the coast. As a result,this taxon has be- perus communis,the proportionof emptyseeds is also come vulnerablein the zone, and restorationprograms markedlyhigh, ranging from 40% to 96% in different have been set in motion.The resultsof our studyhave populations (Houle and Babeux 1994). Owens et al. several implicationsfor the productionand collection (1990) reportedthat if abortiontakes place afterfer- of juniper seeds. It would be appropriateto collect tilization period in Thuja plicata, the empty seeds seeds fromfemale individuals thathave a very close would be externallyindistinguishable from ripe filled mate and are placed in favorable sites. Of the studied seeds. This situationis similar to J. oxycedrus.Main populations,Punta Paloma had the highestnumber of causes of seed abortion at this stage are poor pollen filled seeds per cone, and this population seems to be viabilityor vigor (Owens et al. 1990), or endogamy the most suitable for seed collection. (Sorensen 1982; Owens et al. 1991; Arista and Tala- In conclusion, both subspecies of J. oxycedrusdis- vera 1996). As J. oxycedrus is a dioecious species, play high percentagesof empty seeds per cone. Pop- selfingis ruled out as a cause of abortion.Because of ulations and plants differin their seed viability,and the natureof our work, it is not possible to know the thus preliminaryscreening is necessary to optimize effectof endogamy(crosses betweensiblings) and pol- seed production for restorationpurposes. Moreover, len vigor or viability as sources of empty seeds, but dioecy makes thisspecies more vulnerableto any man- they should not be ruled out. The fact thatthe Puerto agement-alteringsex ratio or mate distances. del Boyar population, situatedin the most xeric site, showed the lowest number of filled seeds per cone Acknowledgments indicates that resource limitationcould be partlyre- We thankDrs. J. N. Owens and D. C. Freeman for sponsible for seed abortion at this stage. In fact, the their useful comments, which improved this manu- investmentin the maturingembryos may be verylarge script. This research was supported by grant 4086 (Willson 1983). Moreover,in J. oxycedrusthe two re- (Ayuda a los grupos de investigacion)from the Junta productivecycles overlap,and two seed cone crops co- de Andalucia and by the Parque NaturalSierra de Gra- occur in an individual. Thus, female individuals re- zalema (Proyecto Pinsapar,A.M.A.). LiteratureCited

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