Dwarf sandwort (Minuartia pusilla) COSEWIC assessment and status report: chapter 6

Biology

General

There has been one study that included mention of Minuartia pusilla (Meinke and Zika 1992), and some work has been done on other similar species. These studies may be used to draw some conclusions about the biology of this species.

Phenology

Minuartia pusilla likely germinates in December or January in British Columbia, and reaches reproductive age within one year (A. Ceska pers. comm.). It potentially over-winters in the seedling stage and therefore behaves as a winter annual with flowers developing in May or June (A. Ceska pers. comm.). Meinke and Zika (1992) state that M. pusilla is a strict ephemeral that is reliant on precipitation both before and during the growing season for germination and longevity.

Although no work has been done on Minuartia pusilla specifically, its lifecycle requirements appear to have similarities to other close taxa within the family. Baskin and Baskin (1987) looked at Arenaria fontinalis, an eastern North American endemic winter annual. They found that dormant seeds in spring required high summer temperatures to promote after-ripening. This after-ripening period released the seeds from dormancy in the fall. Baskin and Baskin (1972, 1976) and Wyatt (1984) observed that high summer temperatures promoted after-ripening of seeds in several species with similar life cycles, including A. uniflora, another winter annual of the eastern United States. In addition, Baskin and Baskin (1987) investigated the effect of vernalization on seeds and found that A. fontinalis seeds flowered without vernalization, but greenhouse experiments showed that plants kept in an unheated greenhouse during the winter were healthier and had higher survivorship than those kept in a heated greenhouse. As is the case in the majority of winter annual species (Baskin and Baskin 1974, 1987), M. pusilla flowering is potentially controlled by temperature and not photoperiod.

Mating systems

Meinke and Zika (1992) report that M. pusilla has tiny flowers that lack nectar glands and also occasionally lack petals. As well, the anthers open prior to floral expansion suggesting that M. pusilla is exclusively self-pollinated.

Speculation on the mating system operating in the British Columbia population of M. pusilla could be based on studies done on other species in the family with similar life cycles. Wyatt (1984, 1986) reported that populations of A. uniflora have a wide range of different mating systems with large-flowered plants predominantly outcrossing in the center of the species range and highly selfing small-flowered pseudo-cleistogamous plants in the peripheral parts of the range. Fishman and Wyatt (1999) found in A. uniflora that selfing was common in plants of ephemeral habitats. Likewise, Lloyd (1965) found that populations that grew on shallow soils were forced to bloom earlier, thereby missing the emergence of pollinating insects. As there is a greater potential for local adaptation by self-pollinating taxa (Jain 1976), it seems that there would be great advantage for an isolated population at the furthest extent of the species range to adopt self-pollination as its mating system. Therefore, given all the above observations, it is likely that Minuartia pusilla is self-pollinating.

Pollinators have not been observed on M. pusilla in British Columbia.  Andrena bees are important pollinators for species of Arenaria. The pollinators of A. uniflora were Dipterans (particularly syrphid flies), Hymenoptera species (particularly andrenid and halictid bees) and one species of Lepidoptera (Wyatt 1986).

Survival

Sharitz and McCormick (1973) found that the early juvenile stages were the most vulnerable period in M. uniflora. This was due to the washing out of seeds and seedlings due to natural precipitation, as well as a demonstrated sensitivity to moisture stress. These two factors both contributed to early mortality. Wyatt (1986) also looked at survivorship in A. uniflora and in dry years, survivorship decreased due to competition for available water. Wyatt (1986) also found that the species was less resistant to abiotic stress than other primary invaders (of granite outcrops). Sharitz and McCormick (1973) found that soil depth and moisture determined plant densities and the outcome of within-species competition. For A. uniflora, Wyatt (1984) found that deeper soils lead to the invasion of other plants that would potentially outcompete smaller species such as Arenaria species.

Physiology

Unknown.

Movements/dispersal

Minuartia pusilla seeds have no mechanisms for dispersal; however, Wyatt (1984) found that seashore birds walking in muddy areas may disperse seeds of A. uniflora. The location of the extant population of M. pusilla in BC is adjacent to the ocean and gulls are known to frequent the area.

Nutrition and interspecific interactions

Unknown.

Behaviour/adaptability

Minuartia pusilla is an ephemeral species and therefore, relies on seasonal precipitation for germination and longevity (Meinke and Zika 1992). It is dependent on consistent year-to-year moisture during the appropriate seasons for both germination and seedling development. We do not know how adaptable the species will be to climate change (i.e. to an increasing drying trend), but it is likely that it will not survive, due to these requirements.

It is unknown how well M. pusilla will tolerate environmental degradation, but since it is a diminutive annual, any small disturbance is likely to interfere with its lifecycle and thereby decrease survival rate. 

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