Interference of Asexual and Sexual Reproduction in the Green Hydra
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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/227073954 Interference of asexual and sexual reproduction in the green hydra Article in Ecological Research · November 2011 DOI: 10.1007/s11284-010-0771-6 CITATIONS READS 17 1,030 1 author: Anita Kaliszewicz Cardinal Stefan Wyszynski University in Warsaw 19 PUBLICATIONS 72 CITATIONS SEE PROFILE All content following this page was uploaded by Anita Kaliszewicz on 16 February 2015. The user has requested enhancement of the downloaded file. Ecol Res (2011) 26: 147–152 DOI 10.1007/s11284-010-0771-6 ORIGINAL ARTICLE Anita Kaliszewicz Interference of asexual and sexual reproduction in the green hydra Received: 15 February 2010 / Accepted: 23 September 2010 / Published online: 3 November 2010 Ó The Ecological Society of Japan 2010 Abstract The green hydra, Hydra viridissima, has three participation of gametes) can also reproduce sexually. sexes: hermaphrodite, male, and female. I investigated Thus, asexual reproduction without involvement of the reproductive strategies of the green hydra and the gametes (e.g., fission, budding, or defragmentation) is relationship between asexual budding and sexual often interrupted by periods of sexual reproduction. reproduction. The proportion of mature individuals in Alternating between sexual and asexual reproduction is the asexually reproducing population increased with common in many freshwater and marine invertebrates, increasing temperature. Sexual reproduction did not such as echinoderms, oligochaetes, polychaetes, nemer- interrupt asexual budding in hermaphrodites or males; tines, platyhelminthes (Christensen 1984; McElhone sexual reproduction did interrupt asexual budding in 1982; McGovern 2002; Riser 1994; Rouse and Pleijel females. Sexual reproduction also resulted in exponen- 2001; Wallace and Benbow 2009), and cnidarians, tial population growth during the reproductive season. such as sea anemones and freshwater hydras (Giese The number of asexual buds on each parental individual and Pearse 1974; Hyman 1940; Pennak 1978). Sexual was positively correlated with the parental individual reproduction appears to be a strategy these animals size in asexual individuals and in males. The same utilize for surviving unfavorable conditions (e.g., in oli- positive correlation was found between the number of gochaetes and hydras; Burnett 1973; Christensen 1984) testicles and the size of males. These correlations reflect or dispersing (e.g., in echinoderms and sea anemones; a common tendency in asexual and sexual reproduction: Shick 1991; Thorson 1950). Sexual reproduction is larger parental individuals have a greater number of usually limited to distinct time periods, and animals can propagules or gametes. No correlation was found begin to reproduce sexually in response to changing between size and buds or size and gonads in hermaph- environmental conditions. Factors that induce sexual rodites; hermaphrodites had at most one asexual bud reproduction include changes in temperature, photope- and were significantly larger than males, females, and riod, and/or food availability (Burnett 1973; Giese and asexual individuals. The larger size of hermaphrodites Pearse 1974; Whitney 1907). Generally the switch from supports the hypothesis that producing both female and asexual reproduction to sexual reproduction is complete; male gonads is more energetically costly than producing individuals stop their asexual reproduction and start only one type of gamete (gonochorism). to develop gonads. There are also hermaphroditic or gonochoric species that reproduce both sexually and Keywords Budding Æ Reproductive strategies Æ asexually. Hermaphroditic species are dominant in Hydras Æ Three sexes Æ Hermaphroditism number and include oligochaetes, nemertines, platyhel- minthes, and most of the cnidarians. Conversely, gonochoric species are less abundant and include the Introduction echinoderms, polychaetes, some sea anemones, and hydras (Giese and Pearse 1974; Hyman 1940). Asexual reproduction in aquatic animals cannot be Hydras can be either hermaphroditic or gonochoric described as a marginal strategy. Many animals that (e.g., Hydra vulgaris and the symbiotic Hydra viridissima can reproduce asexually sensu stricto (without the Pallas 1766, Stagni 1966). H. viridissima is an exception to other hydra species regarding the interference of sexual and asexual periods because asexually reproduc- A. Kaliszewicz (&) ing individuals that start to develop gonads do not Centre for Ecological Research, Polish Academy of Sciences, interrupt their asexual budding even when they have Konopnickiej 1, 05-092 Łomianki, Poland E-mail: [email protected] matured (Burnett and Diehl 1964). H. viridissima 148 (formerly Chlorohydra viridissima Pallas 1766; syn. polyp size measurements, the average of two width and Hydra viridis Linnaeus 1767; Cnidaria: Hydridae) is one length measurements of each H. viridissima individual of the host species for Chlorella algae and can be found was used in Eq. 1. I collected 1,423 H. viridissima sam- in freshwater ponds throughout Europe and other parts ples. Mature individuals and subsamples of asexual of the world (excluding Antarctica). Similar to other individuals (N = 165 polyps) were measured. They were hydras, H. viridissima reproduces primarily by asexual sexed, and the number of gonads and asexual buds budding. In contrast to most European hydra species, was noted. H. viridissima size was compared with the H. viridissima is a ‘‘warm-crisis’’ hydra. H. viridissima number of buds and testicles for males and hermaph- reproduces sexually when temperatures rise to or are rodites. H. viridissima population density was calculated maintained at high levels (‡20°C) (Burnett 1973). The as the number of H. viridissima per 100 g dry mass of the sexual reproductive period of H. viridissima in the tem- plants to which the H. viridissima samples were attached perate zone occurs between May and June. Whitney during collection. The macrophytes were dried at 55°C (1907) reported that increasing temperatures were the for 24 h and then weighed. main factor inducing the development of gonads in H. viridissima. Interestingly, the large H. viridissima individuals developed ovaries and testicles whereas small Statistics individuals only developed testicles (Whitney 1907). Females have been reported as a facultative and mar- The relationship between H. viridissima size and the ginal sex of H. viridissima (Stagni 1966). number of testicles and asexual buds produced by I analyzed the interference of asexual and sexual hermaphrodites and males was evaluated with the non- reproduction and the proportion of three sexes present parametric Spearman’s correlation test. Differences in in H. viridissima. The goals were to assess (1) the density the size of nonbudding and budding H. viridissima of H. viridissima population during the season of their individuals by sex (hermaphrodites, males, and females) presence, (2) the abundance of each sex during the sex- and the proportion of budding individuals to nonbud- ual reproductive period, (3) the time of gonad induction, ding individuals was assessed with Kruskal-Wallis and and the size differences between sexes, and (4) the cor- Mann-Whitney U tests. A significance level of 0.05 was relation between the size of the reproducing individuals assumed for the statistical analyses, which were per- and their number of buds and gonads. formed using the Statistica 6.1 software. Methods Results Sample collection and analysis Population density and proportion of sexual individuals Hydra viridissima were collected from a canal connected Hydra viridissima individuals were found in the canal to the small Jeziorka River in Konstancin Jeziorna, from May to July when temperatures ranged from 15 to central Poland (52°05¢N, 21°08¢E). In the summer, the 25°C. Population growth was exponential during the canal water is covered by a dense Lemna bloom. I col- H. viridissima growing season. At the end of June, I lected H. viridissima samples in three locations (sepa- observed maximum H. viridissima abundance (14,000 rated by more than 15 m) every 10 days from April to individuals per 100 g of dry mass of macrophytes; July in 2008 when H. viridissima were present. The Fig. 1b). The first mature individuals were observed in samples, attached to submerged macrophytes, were May and accounted for less than 5% of the population transported in plastic bags to the laboratory and ana- (Fig. 1a). Throughout the growing season, asexual lyzed within 24 h. The samples were removed by a pip- individuals were the most dominant form of H. viri- ette from the macrophytes and transferred to Petri dissima, and 31% of asexual individuals were budding. dishes. Then, mature H. viridissima and subsamples of The number of buds per individual ranged from 1 to 5. asexual individuals were photographed and measured The size of budding H. viridissima positively correlated with MultiScanBase v. 13.01 software. Because polyps with the number of buds (rs = 0.34, P = 0.001; Fig. 4 can shrink and individuals differ in length, the size of b). The proportion of mature individuals increased with each animal was not measured by column length, the increasing temperature. Sexual individuals represented metric used previously (Forrest 1959; Massaro and less than 16% of H. viridissima during the growing Rocha 2008), but by surface area (AH). H. viridissima season (Fig. 1a). surface area was calculated from the equation of the lateral cylinder