Annual clovers (Trifolium spp.) have different reproductive strategies to achieve persistence in Mediterranean-type climates
Hayley C. Norman A B E , Philip S. Cocks A C and Nick W. Galwey A DA School of Plant Biology and Centre for Legumes in Mediterranean Agriculture, The University of Western Australia, Crawley, WA 6009, Australia.
B CSIRO Livestock Industries, Private Bag 5, Wembley, WA 6913, Australia.
C Present address: CRC for the Plant Based Management of Dryland Salinity, University of Western Australia, Nedlands, WA 6907, Australia.
D Present address: New House, George Green, Little Hallingbury, Bishop's Stortford, Hertfordshire, CM22 7PP, UK.
E Corresponding author. Email: Hayley.Norman@csiro.au
Australian Journal of Agricultural Research 56(1) 33-43 https://doi.org/10.1071/AR03236
Submitted: 12 November 2003 Accepted: 29 November 2004 Published: 31 January 2005
Abstract
The aim of this work was to determine whether different species of annual clover (Trifolium spp.), obtained from the same environment, have different reproductive strategies (combinations of reproductive traits) to achieve ecological success. A better understanding of the traits that improve persistence should allow agronomists to narrow the selection criteria for new clover cultivars for ley-farming systems in southern Australia. Seeds of 18 annual clover species were obtained from 3 Australian and 6 Mediterranean sites and were subsequently grown in a common garden in Western Australia. Reproductive traits, including time of flowering, weight per seed, fecundity, pollen to ovule ratio, and pattern of seed softening, were observed.
Accessions of different clover species from the same site of collection had different reproductive strategies. Across a range of collection sites, accessions of the same species demonstrated the same broad reproductive strategy; however, some traits, e.g. the timing of flowering, varied within species across collection sites. Principal component analysis suggested that there are 3 broad reproductive strategies demonstrated by these clover species. At one extreme were the relatively large-seeded clovers (T. subterraneum, T. clypeatum, and T. stellatum). The associated cost of these large seeds is reduced fecundity. The large-seeded clovers do not have high long-term hardseededness (the predominant form of seed dormancy in clovers). The relatively small-seeded clovers were all characterised by high fecundity. Many of the small-seeded clovers have high levels of long-term hardseededness, which allow the risk of failure to be spread across seasons (T. spumosum, T. hirtum, T. lappaceum, T. angustifolium, and T. tomentosum). Some of the small-seeded clovers (T. glomeratum, T. nigrescens, T. campestre, T. cernuum, and T. suffocatum) are generalists, producing as many seeds as possible in each season, with very little hardseededness.
There are several possible explanations for the apparent success of such different reproductive strategies among clover accessions of different species at the same site. A plant may achieve the same goal by trading one reproductive trait for another. For example, it may either produce many small seeds to spread the risk of failure or produce fewer large seeds with an inherent competitive advantage. Alternatively, temporal and spatial variation may favour clovers with a number of different reproductive strategies. It is likely that a mixture of species with different reproductive strategies will maximise production and persistence of legume-based pastures in ley-farming systems.
Additional keywords: fitness, evolution, ruderal, ley farming, pollen : ovule ratio, natural selection.
Acknowledgments
The authors thank Angelo Loi (Agriculture WA), Brad Nutt (Agriculture WA), Patrick Smith (CSIRO Sustainable Ecosystems), and staff from the School of Plant Biology and the University Research Station (University of WA). Fiona Maley and John Norman provided technical and field assistance. Thank you to Richard Snowball of the Trifolium Genetic Resource Centre, for access to his database and seed. We appreciate the input from the anonymous AJAR referees. The Grains Research and Development Corporation funded this work through a Junior Research fellowship to H. Norman.
Aarssen LW
(1989) Competitive ability and species coexistence: a plant’s eye view. Oikos 56, 386–401.
Aarssen LW, Taylor DR
(1992) Fecundity allocation in herbaceous plants. Oikos 65, 225–232.
Allard RW
(1965) Genetic systems associated with colonising ability in predominantly self-pollinated species. ‘The genetics of colonising species’. (Eds HG Baker, GL Stebbins)
(Academic Press: New York, London)
Arroyo MTK
(1973) Chiasma frequency evidence on the evolution of allogamy in Limnanthes floccosa (Limnanthaceae). Evolution 27, 679–688.
Baker HG
(1967) The evolution of weedy taxa in the Eupatorium microstemon species aggregate. Taxon 16, 293–300.
Barrett SCH, Richardson BJ
(1986) Genetic attributes of invading species. ‘Ecology of biological invasions: an Australian perspective’. (Eds RH Groves, JJ Burdon)
pp. 21–33. (Australian Academy of Science: Canberra, ACT)
Bennett SJ
(1997) Genetic variation between and within two populations of Trifolium glomeratum (cluster clover) in Western Australia. Australian Journal of Agricultural Research 48, 969–976.
| Crossref | GoogleScholarGoogle Scholar |
Bennett SJ
(1999) Ecotypic variation between and within two populations of T. tomentosum (woolly clover) from Syria and Western Australia. Australian Journal of Agricultural Research 50, 1443–1450.
| Crossref | GoogleScholarGoogle Scholar |
Bugg RL
(1995) Cover crop biology: a mini review. Sustainable Agriculture Newsletter (Vol. 7), University of California.
Carleton AE, Cooper CS
(1972) Seed size effects upon seedling vigour of three forage species. Crop Science 12, 183–186.
di Castri F
(1981) Mediterranean type shrublands of the world. ‘Ecosystems of the World 11: Mediterranean-type shrublands’. (Eds F diCastri, D Wgoodall, RL Specht)
(Elsevier Scientific Publishing: Amsterdam)
Cocks PS
(1993) Legumes from the Mediterranean basin: a continuing source of agricultural wealth for southern Australia. Cooperative Research Centre for Legumes in Mediterranean Agriculture, Technical Paper No.1. Perth, Australia.
Cocks PS
(1995) Genotype times site interactions in seed production, hard seed breakdown and regeneration of annual medics (Medicago spp.) in west Asia. Journal of Agricultural Science 125, 199–209.
Cohen D
(1966) Optimising reproduction in a randomly varying environment. Journal of Theoretical Biology 12, 119–129.
| Crossref |
PubMed |
Cohen D
(1967) Optimising reproduction in a randomly varying environment when a correlation may exist between the conditions at the time a choice has to be made and the subsequent outcome. Journal of Theoretical Biology 16, 1–14.
| Crossref |
PubMed |
Cohen D
(1968) A general model of optimal reproduction in a randomly varying environment. Journal of Ecology 56, 219–228.
Cruden RW
(1977) Pollen–ovule ratios: a conservative indicator of breeding systems in flowering plants. Evolution 31, 32–46.
Ewing MA,
Bathgate AD,
French RJ, Revell CK
(1992) The role of crop and pasture rotations on duplex soils. Australian Journal of Agricultural Research 32, 971–979.
Genstat 5 Committee (1993).
Ghassali F,
Osman AE, Cocks PS
(1998) Rehabilitation of degraded grasslands in north Syria: the use of Awassi sheep to disperse the seeds of annual pasture legumes. Experimental Agriculture 34, 391–405.
| Crossref | GoogleScholarGoogle Scholar |
Grime JP
(1977) Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. American Naturalist 111, 1169–1194.
| Crossref | GoogleScholarGoogle Scholar |
Gross KL
(1984) Effects of seed size and growth form on seedling establishment of six monocarpic perennial plants. Journal of Ecology 72, 369–387.
Kemp PR
(1989) Seed banks and vegetation processes in deserts. ‘Ecology of soil seed banks’. (Eds MA Leck, VT Parker, RL Simpson)
pp. 257–281. (Academic Press: San Diego, CA)
Norman HC,
Cocks PS, Galwey NW
(2002a) Hardseededness in annual clovers: variation between populations from wet and dry environments. Australian Journal of Agricultural Research 53, 821–829.
| Crossref | GoogleScholarGoogle Scholar |
Norman HC,
Cocks PS,
Smith FP, Nutt BJ
(1998) Reproductive strategies in Mediterranean annual clovers: germination and hardseededness. Australian Journal of Agricultural Research 49, 973–982.
| Crossref | GoogleScholarGoogle Scholar |
Norman HC,
Galwey NW, Cocks PS
(2002b) Hardseededness in annual clovers: variation within populations and subsequent shifts due to environmental changes. Australian Journal of Agricultural Research 53, 831–836.
| Crossref | GoogleScholarGoogle Scholar |
Nutt, BJ ,
Carr, SJ ,
and
Samaras, S (1996).
Pake CE, Venable DL
(1996) Seed banks in desert annuals: Implications for persistence and coexistence in variable environments. Ecology 77, 1427–1435.
Philippi T
(1993a) Bet-hedging germination of desert annuals beyond the first year. American Naturalist 142, 474–487.
| Crossref | GoogleScholarGoogle Scholar |
Philippi T
(1993b) Bet-hedging germination of desert annuals variation among populations and maternal effects in Lepidium lasiocarpum. American Naturalist 142, 488–507.
| Crossref | GoogleScholarGoogle Scholar |
Ritland K
(1983) The joint evolution of seed dormancy and time of flowering in annual plants living in a variable environment. Theoretical Population Biology 24, 213–243.
| Crossref |
Rossiter RC
(1966) Ecology of the Mediterranean annual-type pasture. Advances in Agronomy 18, 1–56.
Runyeon H, Prentice HC
(1996) Genetic structure in the species pair Silene vulgans and S. uniflora (Caryophyllaceae) on the Baltic island of Oland. Ecography 19, 181–193.
Russi L,
Cocks PS, Roberts EH
(1992) The fate of legume seeds eaten by sheep from a Mediterranean grassland. Journal of Applied Ecology 29, 272–278.
Sinervo B, Svensson E
(1988) Mechanistic and selective causes of life history trade-offs and plasticity. Oikos 83, 432–442.
Smith CC, Fretwell SD
(1974) The optimal balance between size and number of offspring. American Naturalist 108, 499–506.
| Crossref | GoogleScholarGoogle Scholar |
Smith FP,
Cocks PS, Ewing MA
(1995) Variation in the morphology and flowering time of cluster clover (Trifolium glomeratum L.) and its relationship to distribution in southern Australia. Australian Journal of Agricultural Research 46, 1027–1038.
| Crossref | GoogleScholarGoogle Scholar |
Smith FP,
Cocks PS, Ewing MA
(1998a) Seed production in cluster clover (Trifolium glomeratum L.). 1. Flowering time, abortion, seed size, and hardseededness along branches. Australian Journal of Agricultural Research 49, 961–964.
| Crossref | GoogleScholarGoogle Scholar |
Smith FP,
Cocks PS, Ewing MA
(1998b) Seed production in cluster clover (Trifolium glomeratum L.). 2. Effect of sowing time and sowing rate on flowering time, abortion, seed size, and hardseededness. Australian Journal of Agricultural Research 49, 965–971.
| Crossref | GoogleScholarGoogle Scholar |
Stebbins GL
(1957) Self-fertilisation and population variability in the higher plants. American Naturalist 91, 337–354.
| Crossref | GoogleScholarGoogle Scholar |
Thomson EF,
Rihawi S,
Cocks PS,
Osman AE, Russi L
(1990) Recovery and germination rates of seed of Mediterranean medics and clovers offered to sheep at a single meal or continuously. Journal of Agricultural Science, Cambridge 114, 295–299.
Venable DL
(1992) Size number trade-offs and the variation of seed size with plant resource status. American Naturalist 140, 287–304.
| Crossref | GoogleScholarGoogle Scholar |
Watkin BR, Clements RJ
(1977) The effects of grazing pastures on animals. ‘Plant relations in pastures’. (Ed. JR Wilson)
pp. 273–289. (CSIRO Press: Melbourne)
Went FW
(1979) Germination and seedling behaviour of desert plants. ‘Arid-land ecosystems: structure, functioning and management’. (Eds DW Goodall, RA Perry, RL Simpson)
pp. 447–489. (Cambridge University Press: Cambridge, UK)
Williams WA
(1956) Evaluation of the emergence force exerted by seedlings of small seeded legumes using probit analysis. Agronomy Journal 48, 273–274.
Williams WA
(1968) The emergence force of forage legume seedlings and their response to temperature. Crop Science 3, 472–474.
Zohary, M ,
and
Heller, D (1984).
