Most perennial plants are iteroparous. Moreover, most long-lived animals are iteroparous. They produce large and few offspring. Humans are iteroparous organisms.
We are capable of having offspring several times during our lifetime. Similarly, many mammals are iteroparous. Moreover, birds, most fish species and reptiles are iteroparous.
Semelparity is defined by a single, highly fecund bout of reproduction, while iteroparity is defined by repeated bouts of reproduction throughout life. So, this is the key difference between semelparity and iteroparity. Semelparous organisms die after the first reproduction. In contrast, iteroparous organisms live to reproduce repeatedly. Moreover, semelparous organisms are usually short-lived, while iteroparous organisms are usually long-lived. When considering the offspring production, semelparous organisms produce many small offspring, while iteroparous organisms produce large few offspring.
Therefore, this is an important difference between semelparity and iteroparity. Semelparity and iteroparity are two types of reproductive strategies seen in living organisms.
Semelparity refers to the species which die after the first reproduction. The Evolution of Aging. Semelparity and Iteroparity By: Truman P. Citation: Young, T. Nature Education Knowledge 3 10 Why do some organisms die immediately after reproducing some salmon and bamboos, many insects, and all grain crops , while others live on to reproduce repeatedly most plants and vertebrates?
Aa Aa Aa. Figure 1: Semelparous plants. Like all grain crops, wheat is semelparous plant. Dilemma and Cost of Reproduction. Salmon at their spawning grounds, far from the ocean. Theoretical Approaches. These models fall into three classes, all of which assume a tradeoff between reproduction and survival: Demographic models predict that when adult survival is low enough relative to juvenile survival , evolution should abandon withholding resources for a future reproduction that is unlikely, and instead favor semelparity Figure3.
Bet-hedging models predict that when adult survival is highly variable, evolution should favor iteroparity, because it does not risk putting all reproductive effort into a single reproductive episode. Models incorporating non-linear patterns of reproductive costs and benefits predict that semelparity should be more likely to evolve when most of the costs of reproduction reduction in future survival or reproduction caused by increases in current reproduction happen even at low levels of reproductive effort, or conversely, when the benefits of reproduction accrue most rapidly at high levels of reproductive effort.
Figure 3: Schematic of the demographic model of the evolution of semelparity. Imagine semelparous and iteroparous populations. The semelparous annual individuals produce 2. In the first year, the semelparous individuals out-produce the iteroparous, but the iteroparous have some probability of living to reproduce again. Therefore, in populations with sufficiently high mortality, semelparity will be favored over iteroparity. Demographic models of semelparity explore this more explicitly.
Empirical Evidence. There have been several more successful tests of the demographic model, and they all show that semelparity is more likely in species or populations where adult survival would be low even if they were not semelparous. These tests come from diverse systems, including spiders, fish, an alpine mustard, and a giant rosette plant. In addition, both desert annuals and early successional annuals live in habitats where survival beyond the growing season might be expected to be low.
Synchronous Semelparity. Species "Approaching" Semelparity. Semelparity and iteroparity have been represented here as a simple dichotomy. Nevertheless, the conceptual framework can be applied more generally. These include subalpine fir trees, patas monkeys, and several insect species.
Semelparity in Grain Crops. It is probably no coincidence that many herbaceous crops, including virtually all grain crops, are annuals. Their semelparity results in far higher yields than if they were iteroparous. It is likely that when selecting grain species for cultivation, early farmers deliberately chose those species with the highest yields, which were annuals, or selected strongly enough for high yields that iteroparous species evolved into semelparous species.
The closest relatives of both rice and maize are iteroparous. Given our dependence on semelparous species, it is important that we better understand the evolution and physiology of this curious life history. References and Recommended Reading Arizaga, S.
Bell, G. On breeding more than once. American Naturalist , 57—77 Bulmer, M. Theoretical evolutionary ecology. Stearns, S. The Evolution of Life Histories. Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Flag Content Cancel. Email your Friend. Submit Cancel. This content is currently under construction. Explore This Subject. Topic rooms within Evolution Close. No topic rooms are there.
Lead Editor: Nick Bisceglia Evolution. Or Browse Visually. Other Topic Rooms Ecology. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters. The Beyond. Plant ChemCast. Postcards from the Universe. Brain Metrics. Mind Read. A GLMM for mean number of branches showed a highly significant effect of bolting month on number of branches Table 7. Late-bolting plants produced a greater number of branches Figure 2 A,B.
A GLMM for total number of fruit showed a highly significant effect of bolting month on number of fruit Table 8. As plants bolted later in the season, they produced more fruit Figure 2 C,D.
All interaction terms included in the GLMM were also significant predictors of number of fruit. Fruiting traits by bolting date over three years. Number of branches charts A and B represents the mean number of branches per plant by bolting month. Total fruit number charts C and D represents the mean number of fruits per plant by bolting month. Charts on the left A and C show lab results and those on the right B and D show field results. Both seed traits analyzed in this study showed phenotypic plasticity across bolting dates Table 3.
A GLM showed a significant effect of bolting month on seed size Table 9 ; late-bolting plants produced smaller seeds than early-bolting plants Figure 3 A,B.
No other predictors were significant. A GLM showed a significant effect of bolting month on seed number Table Late-bolting plants produced significantly more seeds than early-bolting plants Figure 3 C,D.
Offspring seed traits by bolting date over three years. Seed size charts A and B indicate mean seed length by bolting month data available only for June and September bolting months.
Total seed output charts C and D indicates mean number of seeds produced per plant by bolting month. Reproduction in L.
Variation in the expression of the degree of semelparity was consistent with the continuum hypothesis and inconsistent with the single strategy hypothesis: in lab and field environments alike, reproductive traits varied continuously as plants bolted later on in the season.
June-bolting plants expressed prolonged semelparity where reproductive effort was realized slowly , while September-bolting plants expressed a more instantaneous or extreme semelparity where reproductive effort was realized quickly.
Although there was substantial variation among individual plants that bolted at different times throughout the season, there were no consistent differences among the 21 genetic lineages. Our results support the continuum hypothesis for each of our main predictions with respect to flowering traits. Perhaps most importantly, late-bolters initiated reproduction sooner after bolting and at a smaller size than did early-bolters.
Flowering soon after bolting and flowering at a small size allows a plant to reproduce sooner, but may cause plants to forego fitness gains associated with production of a larger stalk, which can hold more fruit and disperses seeds farther [ 32 ]. That late-bolting plants would trade off such gains for the ability to initiate reproduction sooner and at a smaller size is consistent with the general prediction of the continuum hypothesis that late-bolting plants respond to a constrained reproductive season by adopting a more extreme semelparous reproductive strategy.
Late-bolters also flowered more synchronously, by fruiting in parallel more frequently and producing many more fruit than early bolters. Although producing many flowers simultaneously may increase maximum fecundity, competition for resources between them may eventually lead to diminishing fitness gains for additional flowers [ 33 , 34 ].
Branching and fruiting patterns were phenotypically plastic across bolting groups. Late-bolting plants produced significantly more fruit and more branches than early-bolting plants. This pattern was not necessarily predicted by the continuum hypothesis, but it makes sense in view of the morphology of our study species: producing fruit on multiple branches allowed late-bolting plants to overcome constraints on fruit production related to the growth of the meristem; late-bolters were able to produce flowering in parallel rather than serially along the main stalk.
Greater numbers of fruit also helped late-bolters produce a greater number of seeds—although early-bolters produced larger seeds, the total fecundity of late-bolters was significantly higher than that of early-bolters. Presumably, there is a context-dependent fitness cost associated with branching in L. We speculate that advantages of main stem dominance in early bolters may include better dispersal in taller plants, and higher diversification in timing of seed production, and thus in timing of germination [ 35 ].
For time-constrained plants late in the season, however, branching provides an outlet for reproductive potential that would otherwise be wasted. Larger seeds show reduced dormancy [ 37 ], and are more likely than smaller seeds to germinate and establish rosettes within the same season.
In contrast, late-bolters produced seeds in many fruits simultaneously, realizing higher fecundity at smaller seed size, although small seeds produced late in the season will be required to overwinter before forming rosettes [ 38 — 40 ]. This is likely due to the fact that seeds produced early in life are more likely to survive to reach reproductive maturity [ 3 , 5 , 17 , 36 , 40 — 42 ]. Bolting month was consistently the best predictor of reproductive traits. This signifies that reproductive allocation is phenotypically plastic with respect to time, and that environmental factors related to bolting month i.
The consistency between lab bolting month groups which, although sharing the same photoperiod schedule, were sheltered from various stressors e. Because all bolting month groups were composed of the same 21 genotypic lineages, and genotype was included as an effect in our mixed model design, genotypic differences were excluded as an explanation for differences among bolting groups. Rosette size was included as an effect in our model, but did not consistently predict phenotypic differences between bolting groups, as we would have expected if plant size, or direct effects associated with plant size, largely determined reproductive allocation patterns.
Differences between plant growth environments showed a consistent pattern: relative to lab-grown plants, field-grown plants generally initiated flowering at a larger size, and produced more branches and seeds, but also showed greater variability in reproductive characters.
Year was not a significant predictor of most of our reproductive traits, but where it was, this was presumably due to maternal effects related to seed age e.
For instance, in eastern Canada experienced a warm, abnormally rainy summer, resulting in all field plants flowering at a smaller size, and producing more branches, fruit and seed. Despite the importance of these additional effects, bolting month was the only effect that significantly predicted all reproductive traits in our study.
In conclusion, our data demonstrate that a classically semelparous plant exhibits variation in parity expression that is consistent with adaptive phenotypic plasticity. Other studies [ 13 , 25 ] have shown intriguing evidence of plasticity in reproductive life histories, and here we explicitly test whether plasticity in reproductive behaviour can be explained as plasticity in the expression of parity along a continuum.
That reproductive traits vary predictably with bolting date implies that, in L. This substantiates the notion that there is a meaningful continuum of reproductive traits from a pure semelparous strategy to a prolonged semelparous strategy of iteroparous-like reproductive packaging over a substantial proportion of its lifespan. Conceptual and mathematical models identify the conditions under which annual semelparity has a selective advantage over perennial iteroparity, where semelparous and iteroparous life histories are discrete alternatives.
Our data suggest that these models, because they implicitly consider invariant extreme semelparity and iteroparity, describe the special cases of endpoints of a continuum. Our results suggest that parity may be treated as phenotypically plastic and continuous over shorter time scales, as variation in key reproductive traits yields a life history that falls between the absolute extremes of pure iteroparity and semelparity.
Inferences about the generality of these conclusions will require study of reproductive allocation in other classically semelparous organisms, or in iteroparous organisms in which reliable cues for residual reproductive value may be perceived by individuals. Lobelia inflata Campanulaceae is a monocarpic plant native to Eastern North America.
It has multiple flowering schedules in the wild both annual and biennial patterns have been observed , but reproduction is always semelparous in that the plant senesces after completion of flowering.
Upon germination, L. Outcrossing is prevented by a stamen tube, a structure which permits the release of pollen directly onto the stigma, but does not permit the release of pollen into the air, since it is sealed [ 37 ].
Analyses of polymorphic microsatellite loci [ 44 ] have revealed no evidence that outcrossing occurs in nature. Bolting, which marks the beginning of a transition from a vegetative to a reproductive phase, is irreversible for L. Inflorescences show an acropetal flowering pattern, where flowers are produced in series from the base to the tip of the stalk and along each branch. Reproduction occurs as seeds are formed inside inflated ovules; the number of seeds in a fruit has been observed to depend on environmental unpredictability and reproductive timing [ 39 , 45 ].
During reproduction, one or more shoots may branch off from the main stalk. Seeds disperse passively upon fruit maturation; once all fruits have reached this stage, a plant senesces. Of central importance to our design was the ecological significance of the timing of bolting, marking the irreversible and terminal initiation of reproduction. By manipulating the date of initiation of reproduction, we were able to control the length of time that plants had to reproduce.
Because reproduction is terminated relatively consistently among individuals each year around October 15 th with the onset of hard frosts—a phenotypically plastic reproductive response to a range of manipulated bolting dates could be effected. We collected seeds from dead plants at the Petawawa Research Forest Lat. To maximize the potential inclusion of a variety of genetic lineages and preclude the possible influence of atypical genotypes , we collected seeds from 21 parent plants in the field each at least 50 m from each other.
Each seed sample was used to found an experimental population of genotypically identical replicate plants, yielding 21 potentially distinct genetic lineages. Seedlings were then moved to individual cells dimensions: 7.
Trays were watered twice weekly, and a liquid fertilizer mixture ppm N was added once every two weeks. Seedlings were grown for approximately weeks, forming small rosettes. Rosettes grew undisturbed until bolting; the emergence of a reproductive stalk upon bolting may be reliably detected [ 37 ]; a stalk taller than 4 cm is diagnostic of the onset of bolting. Plants that bolted before the 13 th or after the 17 th of the month were excluded.
The distribution of plants included in the study is shown in Table 1. Lab plants were simply moved into the new chamber in their planting trays, and to minimize the difference in soil conditions between lab and field environments, field rosettes were planted along with the soil from their planting cell. Translocated plants were left to grow, reproduce and eventually senesce. Reproducing plants were monitored every two days until death. Measurements of longest living leaf—a surrogate for rosette biomass [ 43 ], stalk height, stage of flower formation visible bud, anthesis, mature flower, etc… , fruit maturation and branch initiation were performed on growing plants once every days for all plants.
Once they had senesced, plants were taken to the lab, measured, and harvested. At harvest, fruits were measured and removed to storage vials. Seven traits were assessed in this manipulation: three phenological traits, two fruiting and two seeding traits. The three phenological traits were days to first flower, size at first flowering and flowering duration. Flowering duration is the number of days between the formation of the first flower and the maturation of the last flower as it becomes a fruit.
The two fruiting traits included branches per plant and the total number of fruits produced. Upon death of a plant, fruits were counted and fruit location on branch or reproductive stalk recorded. The two seed traits included seed size and the total number of seeds produced.
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