Can nectary structure in Laeliinae promote or constrain nectar secretion?

Area of Science:

• * Botany
• * Plant Anatomy
• * Evolutionary Biology

Background:

• * The orchid subtribe Laeliinae exhibits significant floral morphological diversity.
• * This diversity is linked to pollination ecology, with both insect (entomophilous) and bird (ornithophilous) pollinators.
• * Differences in floral nectary morphology are expected due to varied pollinator interactions.

Purpose of the Study:

• * To compare the inner nectary spur micromorphology in selected Laeliinae genera.
• * To identify structural features influencing nectar secretion and contributing to the subtribe's evolutionary success.
• * To investigate nectary structure in 48 species across Prosthechea, Encyclia, Epidendrum, and Dinema.

Main Methods:

• * Comparative micromorphological analysis of the inner nectary spur.
• * Examination of nectary structure in 48 species from four genera.
• * Statistical analysis of morphological and micromorphological characters related to nectar presence.

Main Results:

• * Nectary shapes varied: narrow-tubular (cuniculus-type) in Encyclia, short sac-like in Prosthechea and Dinema, and both in Epidendrum.
• * Nectar was present in Dinema but absent or variable in Prosthechea, Encyclia, and Epidendrum.
• * Long, tubular nectaries were less likely to contain nectar; sac-like nectaries were more often functional.
• * Nectar presence correlated with a thicker secretory layer and smoother cuticle on epidermal cells.
• * All taxa shared thick cuticles and cell walls in the secretory layer, regardless of nectar presence.

Conclusions:

• * Nectary structure, particularly shape and secretory layer thickness, influences nectar secretion in Laeliinae.
• * Sac-like nectaries and thicker secretory layers are associated with functional nectar production.
• * The presence or absence of nectar suggests secretory capacity is plastic and can be regulated.
• * This plasticity allows for adaptation to varying pollination pressures and contributes to the evolutionary success of the subtribe.