Morphotypes of the lacustrine ostracod Limnocythere rionegroensis Cusminsky & Whatley from Patagonia, Argentina, shaped by aquatic environments

Abstract

This study describes and quantifies morphological valve traits of the ostracod Limnocythere rionegroensis from Patagonian steppe lakes and explores their association with lake water characteristics. Surface ornamentation was examined by scanning electron and transmitted light microscopy, and valve size and shape were analyzed using morphometric techniques. Limnocythere rionegroensis shows remarkable variations in surface ornamentation, based on which three morphotypes (MI, MII, and MIII) were identified. Valves of morphotypes MI and MIII are larger, show slight to moderate external reticulation, and a higher shape variability, whereas MII is characterized by a very conspicuous reticulation, lower shape variability, and smaller valves. Outline analysis yielded a great shape disparity related to the dorsal margin slope. MI was found in sexual populations from euhaline to mesohaline ephemeral lake; MII occurs in parthenogenetic populations from mesohaline to oligohaline permanent or ephemeral lakes; and MIII, from both sexual and asexual populations, inhabits a broad range of environmental conditions in terms of salinity and stability. Limnocythere rionegroensis intraspecific variations may be caused by environmental parameters and genetic factors associated to reproductive strategies. These results contribute to the knowledge of extant L. rionegroensis morphological variability and provide additional clues to improve the environmental interpretation of fossil assemblages.

Impact of climate and hydrochemistry on shape variation – a case study on Neotropical cytheroidean Ostracoda

“…A latest study of Kim et al (Kim et al, 2015) shows that increased levels of pH account for decreased carapace growth rates, i.e., prolonged intermolt periods, and smaller carapaces. Carapace shape changes have been moreover associated with changes in Ca 2+ , Mg 2+ and pH 25 (Ramos et al, 2017). Our analyses, however, revealed correlations neither with ions related to formation of carbonate, such as HCO3 -, Ca…”

“…Frequently identified ecological factors are salinity (Yin et al, 1999;Yin et al, 2001;Grossi et al, 2017) and hydrochemical regime, mirrored by Mg 2+ , Ca 2+ and K + contents (Ramos et al, 2017) or alkalinity and sulphate, 20 respectively (van der Meeren et al, 2010). Morphological response to the same environmental factor may even differ between environments (e.g., Yin et al, 1999), complicating straightforward explanation models.…”

“…A number of studies has shown that ornamentation, noding, sieve pore shape, and carapace size are linked to environmental factors, e.g., salinity, temperature, water depth and nutrient availability (van Harten, 1975;Yin et al, 1999;Majoran et al, 15 2000; van Harten, 2000;Anadón et al, 2002;Frenzel and Boomer, 2005;Medley et al, 2007;Marco-Barba et al, 2013;Meyer et al, 2016;Boomer et al, 2017). Especially with the rise of morphometric techniques, investigations also dealing with carapace shape variation in relation to environmental variables have increased (Yin et al, 1999;Baltanas et al, 2002;Baltanas et al, 2003;van der Meeren et al, 2010;Ramos et al, 2017;Grossi et al, 2017). Yet, the use of morphological data, even those based on morphometric analyses (Baltanas et al, 2002;Baltanas et al, 2003;van der Meeren et al, 2010;Grossi et al, 20 2017), has been restricted to either landmark-based or outline-based studies but have rarely used a combination of both (e.g., Ramos et al, 2017).…”

“…Especially with the rise of morphometric techniques, investigations also dealing with carapace shape variation in relation to environmental variables have increased (Yin et al, 1999;Baltanas et al, 2002;Baltanas et al, 2003;van der Meeren et al, 2010;Ramos et al, 2017;Grossi et al, 2017). Yet, the use of morphological data, even those based on morphometric analyses (Baltanas et al, 2002;Baltanas et al, 2003;van der Meeren et al, 2010;Grossi et al, 20 2017), has been restricted to either landmark-based or outline-based studies but have rarely used a combination of both (e.g., Ramos et al, 2017). Few studies integrate geographic gradients into their statistical analyses and corresponding climate variables or a reduced number of predictor variables.…”

Changes in ostracod assemblages and morphologies during lake‐level variations of Lago Cardiel (49°S), Patagonia, Argentina, over the last 15.6 ka

“…Furthermore, the morphological variability between populations of two widely distributed species, Eucypris fontana (Graf, 1931) and Limnocythere rionegroensis Cusminsky & Whatley, , was determined, allowing further exploration of the relationship between morphological patterns and ecological variables (Ramos et al . , ). Morphological intraspecific variations in ostracod valves are the result of complex interactions between genotype and environment (Baltanás & Geiger ).…”