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Home , Cylindropuntia, Cylindropuntia bigelovii, Propagule, Vegetative reproduction

Patterns of vegetative and distribution of

Ryan Fong1, Lucy Johnson1, Joseph Saucedo2

1University of , Santa Barbara; 2University of California, Los Angeles

ABSTRACT

Cylindropuntia can reproduce sexually, asexually, or both ways, highlighting the spectrum of reproductive strategies within a single . This diversity in reproduction provided an excellent framework for better understanding the distributive differences between sexually and asexually reproducing species within the same habitat. The sole use of in C. bigelovii is not well studied, despite being such an iconic desert species. We investigated factors that might affect vegetative reproduction, such as water content and propagule position. Because C. bigelovii is dispersed by mammals, we also decided to look at how fur type affects ease of dispersal. Finally, we studied whether the patterns of distribution were different between asexually reproducing C. bigelovii and sexually reproducing C. ganderi. Water content had no effect on the force required to remove propagules of C. bigelovii, but propagules on the side dispersed more readily than the top. Propagules attached best to medium length fur, which may indicate that large mammals like coyotes are most responsible for the distribution of propagules. C. bigelovii had a clumped distribution compared to the more even distribution of C. ganderi, suggesting that C. bigelovii may outcompete other cacti due to its vegetative reproduction and its dispersal by mammals. Overall, we propose that asexual reproduction allows C. bigelovii to populate the landscape more effectively than the sexually reproducing C. ganderi.

Keywords: , distribution, asexual reproduction, , dispersal

INTRODUCTION the ways that asexually reproduce is through vegetative reproduction, which Sexually reproducing plants dominate our occurs when a piece of the parent world. Despite the many benefits sexual becomes detached and develops into a new reproduction provides, such as genetic genetically identical individual. Asexual recombination, there are still plants that reproduction can also be beneficial to have evolved to reproduce solely through plants because no pollinator is needed for asexual means (Mandujano 2002). One of reproduction to occur (Urry et al. 2017). In

CEC Research | https://doi.org/10.21973/N3FD3M Fall 2019 1/9

arid and extreme habitats like deserts, onto the ground. Little work has been done vegetative reproduction also allows plants on the effect fur type may have on the ease to circumvent creating delicate , of propagule dispersal; however, it is known which are susceptible to environmental that the high spine density of C. bigelovii stresses (Urry et. al 2017). allows for greater dispersal by animals Studying the differences between sexually compared to other members of Cylindropuntia and asexually reproducing plants can (Bobich 2001). In addition, it has been highlight why some species forego the shown that plant burrs adhere to different benefits of , such as types of fur with varying levels of strength, environmental adaptation through genetic but it is unknown whether the same is true recombination, in favor of vegetative for C. bigelovii (Kulbaba et al. 2009). propagation. Cylindropuntia consists of cacti The way C. bigelovii is dispersed and its that reproduce sexually and others that distribution patterns are particularly reproduce vegetatively (Benson 1982). important to the desert ecosystem because Some cacti in the genus, like Cylindropuntia of the effect it has on the density of the ganderi, or Gander’s cholla, reproduce , Neotoma lepida. These rats solely through sexual reproduction (Bobich use C. bigelovii as an essential source of and Nobel 2001). Others, like Cylindropuntia food, water, and protection for their dens, bigelovii, reproduce through asexual and as such, the density of the woodrat is reproduction. Sometimes referred to as correlated closely to the density of the “jumping cholla” or “teddy bear cholla,” this (Brown 1972). icon of the has barbs on its In this study we chose to examine factors spines that easily attach to the fur of that affect ease of dispersion of C. bigelovii passing mammals (Bobich and Nobel 2001). propagules, the effect of fur length on C. bigelovii is a particularly interesting mammalian distribution of the cactus, and example of asexual reproduction due to it’s the distribution of C. bigelovii in comparison dependance on mammals for dispersal. The to the distribution of C. ganderi. First, we factors that affect the ease of dispersal of assessed the effect of water content on the this cactus are not well understood. A ease of dispersal a vegetative propagule. previous study found that drought over a We hypothesized that plants with more long period of time negatively affects water would drop their propagules easier, C. bigelovii population density; therefore, it both because the propagules weigh more may be useful to observe the effect of and because prior studies on C. bigelovii water content on the ease of its truncata have suggested dispersal (Bobich et al. 2014). Another that cacti with less water are less likely to factor that may impact its dispersal is the reproduce (Heins et al. 1981). The effect of type of fur that comes in contact with the propagule position on the ease of removal cactus during its secondary dispersal. from fur was also tested. We predicted that Secondary dispersal refers to the the propagules on the side of the plant movement of propagules while attached to would remove with less force than the ones the fur of mammals, while primary dispersal on the top because the propagules on the describes the growth of new C. bigelovii side of the cactus are more likely to come in stems from propagules that have dropped contact with passing mammals, and

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because the propagules on the top of the substrate in this area was mostly sand and cactus are not mature enough to be easily granitic gravel. detached (Rebman 2001). In addition, we In order to test the effect of water tested the effect of fur length on the ease content and propagule position on the ease of propagule dispersal. We predicted that it of dispersal, we tested C. bigelovii between would be hardest to remove the cactus 0.8 m and 1.0 m tall. We chose propagules from the longest fur length, and that it that were farthest from the ground for our would be easiest to remove the cactus from “top” measurement and chose propagules the shortest fur. Because the long fur has a farthest away from the trunk of the cactus larger surface area, we predicted that the four our “side” measurement. We then barbs on the spines would adhere most used two spring scales rated at 100 g and strongly to the long fur (Aragón 2007). We 2500 g, attached with about 0.3 m of tooth also examined the distribution of C. floss, to tug on the propagules until they bigelovii compared to C. ganderi, came free from the parent plant. Both hypothesizing that C. bigelovii would have a scales were used interchangeably based on more clumped distribution due to its clonal the strength of propagule attachment. Top reproductive strategy. Finally, we examined propagules were pulled first, followed by the germination success of C. bigelovii the side propagules. One detached propagules dropped on the ground, propagule was cut into a 10 mm3 cube and predicting that cacti with more dropped weighed on a field balance to serve as a propagules would have a higher density of proxy for water content. clones surrounding them. Using one detached propagule per plant, we then used three different materials to METHODS replicate the fur of potential mammals related to C. bigelovii dispersal. The three This study was conducted at Anza- materials consisted of a felt sheet, a Borrego Desert State Park in San Diego medium fur sheet with fur about 3 cm and a County within three sites. One site, along long fur sheet of fur of around 5 cm long. Yaqui Pass Road (33.1804 N, -116.335 W), We chose a variety of fur lengths because was a low elevation desert plain with previous research has indicated that burrs intermixed C. bigelovii and C. ganderi stick to different types of fur with varying populations in packed dirt and sandy levels of strength, and we believed the substrate. Another site, along Montezuma same might be true for cacti because of Road (33.2257 N, -116.425 W), had similarly their barbed spines (Kulbaba, et al. 2009; mixed cacti population, but was located on Aragón 2007). All sheets were equally sized a slope at an elevation of about 600 m and at 22.9 cm by 30.5 cm. A thin sheet of craft had a substrate of granite and quartz. Our foam was added under each material to last sampled site was a hiking trail with simulate skin. The material and foam layers intermediate elevation, called Cactus Loop were pushed on top of the C. bigelovii Trail (33.1389 N, -116.375 W), with dense propagules to attach the cactus to the quantities of C. bigelovii along the ridges material. The propagules were then pulled and C. ganderi bordering the trail. The off using the spring scale and floss in order to measure the detachment force.

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To compare distribution success between effect of primary dispersion counts on sexually and asexually reproducing C. ganderi and C. bigelovii, we ran a two- Cylindropuntia, we counted the number of way ANOVA using the density of each cacti neighboring focal C. bigelovii and species of Cylindropuntia across the 10 m C. ganderi individuals. The counts were first and 2 m radii. The number of propagules on done within a 2 m radius and then within a the ground was compared to the number of 10 m radius away from the chosen plant, plants within 2 m using a linear regression resulting in a circular area of 12.57 m2 and model. 301.43 m2, respectively. From this point, we converted our counts to densities by RESULTS dividing the number of individuals counted at each radius by the circular area of the In total, we sampled 20 C. bigelovii for radius. Each selected C. bigelovii was position and material data, 60 C. ganderi between 0.8 m and 1.0 m high while and 47 C. bigelovii for our distribution data, C. ganderi was between 0.4 m and 0.6 m and 47 C. bigelovii for our vegetative high. The number of cacti counted in the 2 reproduction data. There was no effect of water content on force required to remove m circle were not re-counted in the circle 2 with the 10 m radius to distinguish between each propagule (N = 20, r = 0.06, p = 0.30; close aggregation and further dispersal. To Figure 1). However, it was easier to remove determine primary dispersal success, we propagules from the side of the C. bigelovii also counted the number of propagules than from the top (N = 20, t = 2.54, p = present on the top of the plant and 0.0201; Figure 2). It took the greatest force propagules on the ground within 1 m of to remove a propagule of C. bigelovii from the plant. our medium fur length material (N = 20, F = Statistical analyses were conducted in 21.52, p < 0.01; Figure 3), though both the JMP 14 Student Edition. We used a linear felt and the long fur sheet took an equal regression to test the effect of water amount of force to remove. The number of content on the force required to remove propagules on the ground had a positive correlation with the number of plants the propagules of cactus. A paired t-test 2 analysis was used to determine the effect of within two meters (N = 47, r = 0.14, p = top or side propagules on the ease of 0.009; Figure 4). C. ganderi had no removal from the plant. A one-way ANOVA difference between 2 m and 10 m, but C. was performed to assess the effect of bigelovii had substantially more cacti within material on the force required to remove a 2 m than 10 m. (N = 214, F = 62.40, p = propagule of C. bigelovii. In order to test the 0.0001; F = 72.34, p=0.0001; F = 34.50, p = .0001; Figure 5).

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Figure 3. Effect of material on the force required to remove cactus propagules. Bars represent the average force, in grams, required to pull pieces of cactus off sample fur material. Error bars represent Figure 1. Effect of water on force required to + 1 S.E. Medium-length faux fur was the hardest to remove C. bigelovii propagules. Cube weight refers 3 remove from the cactus. The same amount of force to the 10 mm cubes of cactus that were cut up was required to remove short and long fur (N = 20, F during the experiment. The weight of the cubes was = 21.52, p = 0.0001). used as a proxy for relative water content, with a higher weight indicating greater water content. There was no correlation between cube weight and the force required to remove joint propagules (N = 20, r2 = 0.06, p = 0.30).

Figure 4. Relationship between propagules on the Figure 2. Effect of segment position on the force ground and C. bigelovii within 2 m from the parent required to remove cactus propagules. The bars plant. There is a positive correlation between the indicate the average force, in grams, required to pull number of propagules on the ground and the the pieces of cactus from the plant. Error bars number of C. bigelovii within 2 m of the parent represent +1 S.E. The propagules on the top of the cactus. The more propagules on the ground, the cactus were harder to pull off than the propagules more clones within 2 m of the parent (N = 47, on the side (N = 20, t = 2.54, p = 0.0201). r2 = 0.14, p = 0.009).

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Although water content had no effect on the ease of propagule removal, the position at which a propagule is located on the plant determined the ease of dispersal. The propagules on the side of the plant detached much easier than those on the top of the plant. The ease of detachment for propagules on the side contribute to already established findings of the high competitive ability of C. bigelovii, where dropped C. bigelovii propagules were much more likely to take and sprout Figure 5. The difference in distribution between C. compared to other Cylindropuntia species bigelovii and C. ganderi. The dark bars represent (Ebert 2006). Because C. bigelovii readily cactus density 2 m away from the parent cactus, and drops propagules and these propagules the light bars represent cactus density 10 m away root easily, the plant is able to have from the parent plant. C. ganderi density did not differ between 2 m and 10 m, but C. bigelovii had particularly rapid rates of reproduction. substantially more cacti within 2 m than 10 m Our study also found that C. bigelovii (N = 214, F = 52.84, p = 0.0001). propagules adhered strongest to the medium length fur material. The felt sheet DISCUSSION was likely not as effective at propagule retention because it lacked enough Our findings suggest that asexual substance to attach to the spines. On the reproduction helps C. bigelovii easily other hand, the fur on the long fur sheet disperse across the desert leading to dense may have been too long, causing the populations. Our findings also suggest that propagules to be unable to reach far mammals in the desert with medium length enough to pierce the craft foam. The long fur, such as the coyote, may be the main fur was also not as dense as the medium dispersers of the cacti (Silverstein 2005). length fur, which would have provided less There was no correlation regarding the surface area for the barbs to grab on to. effect of water content on ease of dispersal, Because coyotes have fur that is the most which may mean that C. bigelovii similar to our medium length fur, it is reproduction is not affected by drought possible that the propagules stick to them conditions. It seems that the water content for the longest amount of time (Silverstein had no real impact on the ease of dispersal, 2005). This may suggest that coyotes are perhaps as a result of a low proportion of the main long-distance dispersers of water storage tissues to propagule length in C. bigelovii. C. bigelovii (Gibson and Nobel 1986). In The results of our distribution general, C. bigelovii do not vary much in observations show that the asexual C. their water content, regardless of bigelovii has a more clumped distribution geographic location, as a result of its low than the sexually reproducing C. ganderi. volume of water storage tissues (Bobich, The propagules on the ground near the 2014). subject plant correlated positively with the

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amount of clonal plants present 2 m away, conventional means. The Neotoma genus suggesting that the C. bigelovii tends to heavily depend on a plant species for grow near its parent plant. Additionally, we shelter and food, and often mirror their found that there were substantially more population size to the density of the host C. bigelovii within 2 m of the subject plant plant (Bleich and Schwartz, 1975). This than within 2 m of the C. ganderi subject pattern likewise applies to N. lepida in the plant. The tendency of C. bigelovii to clump, desert, where it was found they travel paired with its high competitive ability, greater distances in search of C. bigelovii favors the formation of dense stands of the and use propagules for their dens and as a species. C. bigelovii can also experience food source. (Brown et al. 1972). As a rapid growth in their population because of result, areas that are suitable habitats for their vegetative reproduction (Mandujano N. lepida may introduce larger populations et al. 2001). Thanks to its combination of of C. bigelovii than would have originally clumped dispersal and high competitive been present. In addition, predators, such ability, when C. bigelovii is dispersed to a as the coyote, that seek to forage through new location it may lead to a dramatic desert woodrat nests, are likely to come change in the flora of the landscape over a into contact with the C. bigelovii propagules relatively short time. C. bigelovii may placed around the den, thus dispersing accumulate and form dense populations, them (Vaughns and Schwartz, 1980). This outcompeting other cacti. Compared to further supports our hypothesis that sexually reproducing C. ganderi, C. bigelovii coyotes are the main long-distance displays a greater reproductive success dispersers of C. bigelovii. based on their abundance and distribution, Our study aims to enrich current in part due to their asexual dispersal knowledge regarding C. bigelovii strategies (Jon 2015). reproductive strategy and distribution To compensate for its lack of dispersal across a landscape. C. bigelovii is a species through pollinators, C. bigelovii asexual that may outcompete other cacti when it reproduction methods have developed to reaches a new habitat due to its rapid compete with other desert plants. Its high production of vegetative propagules. Future potential to resprout and its high aggregate studies could be done to investigate the density may also be important to the rate of establishment within populations of survival of the species within deserts. Due C. bigelovii compared to other species of to its low propensity to retain water within Cylindropuntia. By observing many different its flesh, C. bigelovii has been predicted to species of Cylindropuntia, we would be able experience high mortality rates during to support the hypothesis that C. bigelovii is periods of extreme drought (Bobich et al. able to outcompete them because of its 2014). Combined with the low genetic asexual reproduction. Furthermore, studies diversity that comes with asexual could be done to focus on the long-term reproduction, the high colonization rate effects of variation in water availability on may be its main survival mechanism. the reproductive ability of C. bigelovii. Our C. bigelovii may also be involved in mutual study was not able to capture a wide interactions with the desert woodrat N. variation in water content of the cactus lepida to spread its propagules farther than because of a limited time scale. However, a

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study done over the course of a few years Bobich, E. G. and P. S Nobel. 2001. Vegetative would be able to create a more complete reproduction as related to biomechanics, morphology and anatomy of four cholla cactus story for the effects of drought on species in the Sonoran Desert. Annals of C. bigelovii. In addition, observational 87:485–493. research on mammals that distribute the cactus could determine whether coyotes Bobich, E. G. and P. S. Nobel. 2001. Biomechanics are truly the main secondary dispersers of and anatomy of cladode junctions for two (Cactaceae) species and their hybrid. American C. bigelovii. In general, future studies on Journal of Botany 88:391–400. C. bigelovii could benefit overall scientific understanding of asexual reproduction, and Bobich, E. G., N. L. Wallace, and K. L. Sartori. 2014. the way that the cactus’ physiology Cholla mortality and extreme drought in the interacts with the world around it. Sonoran Desert. Madroño 61:126–136. Brown, J. H., G. A. Lieberman, and W. F. Dengler. ACKNOWLEDGMENTS 1972. Woodrats and cholla: dependence of a small mammal population on the density of cacti. This work was performed at the 53:310–313. University of California’s Steele/Burnand Anza Borrego Desert Research Center doi: Cook, R. E. 1979. Asexual reproduction: a further 10.21973/N3Q94F. We give a special thanks consideration. The American Naturalist 113:769– 772. to the reserve manager Jim Dice for allowing us to conduct research on the Ebert, T.A. 2005. Density dependent responses of University of California, Irvine property. We cacti, Cylindropuntia bigelovii and C. echinocarpa also appreciate Tim Miller, Krikor Andonian, (Cactaceae), in the desert of , and Reina Heinz for guidance throughout USA. Journal of Arid Environments 64:609–619. the process of this study. Harberd, J.D. 1962. some observations on natural clones in Festuca ovina. The New Phytologist REFERENCES 61:85–100.

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