Seedling performance covaries with dormancy thresholds: maintaining cryptic seed heteromorphism in a fire-prone...

Area of Science:

• Ecology
• Evolutionary Biology
• Plant Science

Background:

• Seed heteromorphism, the production of seeds with varying characteristics by a single plant, is hypothesized to be adaptive in disturbance-prone environments.
• In fire-prone ecosystems, seed heteromorphism often relates to varying temperature requirements for breaking physical dormancy, linked to fire severity and soil heating.
• Mechanisms maintaining seed heteromorphism, particularly how selection favors different seed morphs, require further investigation.

Purpose of the Study:

• To test the hypothesis that differential post-fire resource conditions select for covarying seedling traits, thereby maintaining seed heteromorphism.
• To investigate if seed dormancy-breaking temperature thresholds are linked to seedling performance under varying competitive conditions.
• To determine if seed heteromorphism in dormancy-breaking temperature is cryptic, with no obvious morphological differences between morphs.

Main Methods:

• Identified high and low-temperature threshold seed morphs using dormancy-breaking heat treatments and germination trials in two plant species.
• Compared seed mass and other morphological traits between identified seed morphs.
• Grew seedlings from different morphs under both competitive and non-competitive conditions, measuring growth and biomass allocation to assess performance.

Main Results:

• Seedlings from low-temperature threshold seeds exhibited superior performance, particularly under competitive conditions, compared to high-threshold counterparts.
• No significant differences in seed mass or external morphology were observed between the high and low-threshold seed morphs, indicating cryptic heteromorphism.
• Demonstrated that varying post-fire environmental conditions can selectively influence seedling performance, providing a mechanism for maintaining heteromorphic variation.

Conclusions:

• Seed heteromorphism, specifically in dormancy-breaking temperature thresholds, is maintained by selection pressures related to post-fire environmental conditions and seedling competitiveness.
• Cryptic heteromorphism, where morphs are not visually distinct, plays a role in the adaptive strategy of seed dormancy variation.
• The study provides evidence for a mechanism maintaining seed heteromorphism, highlighting the adaptive significance of varied seed traits in dynamic ecosystems.