Fixed Rates of Random Ovule Abortion in Cryptantha Flava (Boraginaceae) and Its Possible Relation to Seed Dispersal Author(s): Brenda Bowers Casper and Delbert Wiens Source: Ecology, Vol. 62, No. 3 (Jun., 1981), pp. 866-869 Published by: Wiley on behalf of the Ecological Society of America Stable URL: https://www.jstor.org/stable/1937752 Accessed: 02-05-2020 17:41 UTC REFERENCES Linked references are available on JSTOR for this article: https://www.jstor.org/stable/1937752?seq=1&cid=pdf-reference#references_tab_contents You may need to log in to JSTOR to access the linked references. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms Ecological Society of America, Wiley are collaborating with JSTOR to digitize, preserve and extend access to Ecology This content downloaded from 130.212.18.96 on Sat, 02 May 2020 17:41:05 UTC All use subject to https://about.jstor.org/terms 866 NOTES AND COMMENTS Ecology, Vol. 62, No. 3 males meet the added costs of harem defense on a Emlen, S. T., and L. W. Oring. 1977. Ecology, sexual se- day-to-day basis by increasing their nightly con- lection, and the evolution of mating systems. Science 197:215-223. sumption of fruit. An A. jamaicensis utilizes about Gill, F. B. 1978. Proximate costs of competition for nectar. 30% of the 26 kJ in a 10-g F. insipida fruit (Morrison American Zoologist 18:753-763. 1980). From previous studies (Morrison 1978a) we LeBoeuf, B. J. 1974. Male-male competition and reproduc- know that nonlactating females and nonharem males tive success in elephant seals. American Zoologist 14:163-176. carry away about seven figs per night, enough to cov- McCracken, G. F., and J. W. Bradbury. 1977. Paternity and er the daily costs of resting metabolism (37 kJ) plus genetic heterogeneity in the polygynous bat, Phyllosto- 1 h of flying (16 kJ). In contrast, a harem male which mus hastatus. Science 198:303-306. fed exclusively from F. insipida trees for seven nights McNab, B. K. 1969. The economics of temperature regu- took 9-1 3 figs per night ( x = 10.9 + 1.8). These were lation in Neotropical bats. Comparative Biochemistry and Physiology 31:227-268. sufficient to cover his resting metabolism and his 1976. Seasonal fat reserves of bats in two tropical 2.9 + 1.1 h of flying. In addition, the numbers of figs environments. Ecology 57:332-338. taken per night were significantly correlated with Morrison, D. W. 1978a. Foraging ecology and energetics nightly flying times (Spearman r*, = 0.826, P < .05). of the frugivorous bat Artibeus jama/censis. Ecology 59:716-723. Harem males apparently adjust their food intake to . 1978b. Lunar phobia in a Neotropical fruit bat, Ar- balance the energy they expend. tibeus jamaicensis. Animal Behaviour 26:852-856. Quantitative studies of the economics of defending . 1979. Apparent male defense of tree hollows in the territories and mates have been limited because of fruit bat Artibeus jamaicensis. Journal of Mammalogy the shortage of natural systems in which one can 60:11-15. 1980. Efficiency of food utilization by fruit bats. measure both energy intake and energy expendi- Oecologia 45:270-273. tures. Such studies to date have focused primarily on Thomas, S. P. 1975. Metabolism during flight in two species territoriality in nectar-feeding birds. Fruit bats provide of bats, Phyllostomus hastatus and Pteropus gouldil. a valuable new system for developing and testing Journal of Experimental Biology 63:273-293. Wells, K. D. 1978. Territoriality in the green frog (Rana ideas in this field. clamitans): vocalizations and agonistic behaviour. Animal Acknowledgments: We thank G. H. Adler for field Behaviour 26:1051-1063. assistance, A. S. Rand for the loan of his night viewing Manuscript received 26 August 1980; revised 10 scope, C. 0. Handley, Jr. and the Smithsonian Trop- November 1980; accepted 18 November 1980. ical Research Institute for logistical support, and J. 2 Department of Zoology and Physiology, Rutgers W. Bradbury, R. C. Lederhouse and K. D. Wells for University, Newark, New Jersey 07102 USA. 3 New Jersey Medical School, College of Medicine and helpful comments on the manuscript. The study was Dentistry of New Jersey, Newark, New Jersey 07103 supported by the National Geographic Society. USA. Literature Cited Bradbury, J. W., and S. L. Vehrencamp. 1977. Social or- ganization and foraging in emballonurid bats. Ill. Mating systems. Behavioral Ecology and Sociobiology 2:1-17. sufficient resources are often implicated as causal Ecology, 62(3), 1981, pp. 866-869 ? 1981 by the Ecological Society of America factors. We propose that in some species a percent- age of the ovules always abort, regardless of ade- quate pollination or favorable environmental condi- tions. We demonstrate that in Cryptantha flava (A. FIXED RA TES OF RANDOM OVULE Nels.) Payson, embryonic development is generally ABORTION IN CRYPTANTHA FLAVA initiated in at least three of the four ovules of each ovary, although most flowers mature only a single (BORAGINACEAE) AND ITS seed. Furthermore, ovule abortion occurs at random POSSIBLE RELA TION TO SEED with respect to position within the ovary and is not DISPERSAL 1 apparently a phenotypic response to environmental factors. Brenda Bowers Casper and Delbert Wiens2 The idea that ovule abortion may function as an adaptive feature in flowering plants has received little Flowering plants commonly produce many ovules attention. In perennial species of Cryptantha a re- that do not develop into seeds. A portion of the ovules duced seed set per flower is correlated with the reten- within an ovary, entire fruits, or even whole inflores- tion of the seeds in the calyx which acts as the disper- cences may fail to mature. Lack of pollination or in- sal unit. Abortion, in this case, may be adaptive for This content downloaded from 130.212.18.96 on Sat, 02 May 2020 17:41:05 UTC All use subject to https://about.jstor.org/terms June 1981 NOTES AND COMMENTS 867 -D N=39 . N=1800 X 15 75 0 E CD u0 O 10- 50 0 0 C 25 6 5- 4) z C. <.5% 0 1 2 3 4 0 1 2 3 4 No. embryos per flower No. mature nutlets per flower FIG. 1. Distribution of mature nutlets per flower for Cryp- FIG. 2. Number of embryos initiated per ovary in Crypt- antha flava. tantha flava. Three hundred flowers (150 pin, 150 thrum) were collected in 1979 from each of six populations in east- ern Utah. ined, any unpollinated flowers were not included in this sample. greater dispersal by wind and thus reduced competi- Two-thirds of the ovaries sectioned contained tion with sibs and parents. young embryos (usually in the early globular stage) Cryptantha flava is a perennial herb widely distrib- in either three or four of the ovules (Fig. 2). Embryos uted throughout the arid Colorado Plateau of eastern within a single ovary often varied considerably in Utah, USA, and parts of adjoining states. Seed pro- size. In some ovules endosperm had disintegrated, duction data obtained in 1979 from six populations and the embryos were obviously collapsed while oth- located throughout much of the range of the species er developing ovules within the same ovaries ap- (an area approximately 200 x 1 100 km) revealed that peared normal (Fig. 3). Only a few ovules lacking flowers generally produce one seed (nutlet), some- embryos contained endosperm, which is also evi- times two nutlets, and only rarely three (Fig. 1). Other dence of fertilization; most appeared to contain un- perennial species of Cryptantha occurring sympatri- fertilized embryo sacs. In some ovules that were ab- cally with C. flava (e.g., C. flavoculata) generally normally shaped, embryo sacs had not formed. mature all four nutlets. Although C. flava is heterosty- The factors limiting seed maturation in natural lous, it is nevertheless self-compatible (B. Casper, species are no doubt numerous and complex. Cer- personal observation), and no difference was found tainly environmental parameters, including the avail- in the distribution of nutlets per flower for pin and ability of resources, may be largely responsible for thrum individuals (Kolmogorov-Smirnov two-sample the occasional low seed sets found in many species. test, D = .028, n, = 900, n2 = 900, P> .10). The regular reduction in seed number per flower in Each ovule within an ovary appears equally likely C. flava, however, appears to be genetically con- to develop. This is demonstrable by observing the trolled. Because the seed set pattern in C. flava is position of developing ovules in flowers that mature consistent throughout the geographic range of the two nutlets. The four nutlets in borages are arranged species, it is unlikely that the pattern is a phenotypic in a square. Thus if ovules develop at random, pairs response to environmental factors. Furthermore, of adjacent nutlets should be twice as common as hand-pollinated plants grown in the greenhouse un- nutlets opposite each other, since there are four com- der regular watering and fertilization regimes typi- binations of two adjacent nutlets and only two ways cally fail to mature more than two seeds per flower, of obtaining opposite nutlets. A X2 analysis of oppo- although all four ovules may initiate development (B. site vs. adjacent positions (n = 219) reveals that Casper, personal observation).