FOURIER TRANSFORM INFRARED MICROSPECTROSCOPY AS A TOOL TO IDENTIFY MACROALGAL PROPAGULES¹

Abstract

Understanding of macroalgal dispersal has been hindered by the difficulty in identifying propagules. Different carrageenans typically occur in gametophytes and tetrasporophytes of the red algal family Gigartinaceae, and we may expect that carpospores and tetraspores also differ in composition of carrageenans. Using Fourier transform infrared (FT-IR) microspectroscopy, we tested the model that differences in carrageenans and other cellular constituents between nuclear phases should allow us to discriminate carpospores and tetraspores of Chondrus verrucosus Mikami. Spectral data suggest that carposporophytes isolated from the pericarp and female gametophytes contained κ-carrageenan, whereas tetrasporophytes contained λ-carrageenan. However, both carpospores and tetraspores exhibited absorbances in wave bands characteristic of κ-, ι-, and λ-carrageenans. Carpospores contained more proteins and may be more photosynthetically active than tetraspores, which contained more lipid reserves. We draw analogies to planktotrophic and lecithotrophic larvae. These differences in cellular chemistry allowed reliable discrimination of spores, but pretreatment of spectral data affected the accuracy of classification. The best classification of spores was achieved with extended multiplicative signal correction (EMSC) pretreatment using partial least squares discrimination analysis, with correct classification of 86% of carpospores and 83% of tetraspores. Classification may be further improved by using synchrotron FT-IR microspectroscopy because of its inherently higher signal-to-noise ratio compared with microspectroscopy using conventional sources of IR. This study demonstrates that FT-IR microspectroscopy and bioinformatics are useful tools to advance our understanding of algal dispersal ecology through discrimination of morphologically similar propagules both within and potentially between species.

Attachment strength differs amongst life‐history stages of an intertidal, isomorphic red alga

“…Diploid tetrasporophytic fronds with non‐gelling λ‐carrageenan (Bellgrove & Aoki ; Bellgrove et al . ) were mechanically weaker and more easily broken than the haploid gametophytic fronds, containing gelling κ‐carrageenan (Bellgrove & Aoki , Bellgrove et al . ).…”

“…) were mechanically weaker and more easily broken than the haploid gametophytic fronds, containing gelling κ‐carrageenan (Bellgrove & Aoki , Bellgrove et al . ). These results provide support for the model that differences in cell‐wall biochemistry (possibly in relation to carrageenans) between gametophytes and tetrasporophytes influences the mechanical strength of fronds.…”

“…; Bellgrove et al . ). However, despite these well‐documented dissimilarities in carrageenans of gametophytes and tetrasporophytes in these families, few studies have examined potential disparity in biomechanics between life‐history phases (but see Carrington et al .…”

“…The cell walls of species within the Gigartinaceae, as well as several other families within the Gigartinales, contain carrageenans. Species within the Gigartinaceae have been shown to possess different carrageenans in alternate life-history phases, the significance of which is currently unknown: the haploid gametophytes have primarily gelling κ-carrageenan, whereas the diploid tetrasporophytes have non-gelling λ-carrageenan (McCandless et al 1983;Bellgrove et al 2009). However, despite these welldocumented dissimilarities in carrageenans of gametophytes and tetrasporophytes in these families, few studies have examined potential disparity in biomechanics between life-history phases (but see Carrington et al 2001).…”

“…The Japanese red alga Chondrus verrucosus Mikami has a triphasic, isomorphic life cycle (Taylor & Chen 1994) with the characteristic life-phase differences in carrageenan contents (Bellgrove & Aoki 2008;Bellgrove et al 2009). Chondrus verrucosus is fertile year round with no clear seasonal peaks (Bellgrove & Aoki 2008), but has large monthly fluctuations in the number of fertile spermatangial, carposporangial and tetrasporangial fronds (Bellgrove & Aoki 2008), which appear to be frequently dislodged.…”