My research focuses on two primary areas of investigation: elucidating the interaction between paleobiogeography, paleoecology, and macroevolution during episodes of biotic overturn and phylogenetic and taphonomic analysis of evolutionary patterns in brachiopods and crustaceans.  Research emphasizes development and implementation of quantitative analytical methods, particularly developing applications of GIS methods for use in paleobiogeography, phylogenetic reconstruction, and paleobiologic inferences based on phylogenetic hypotheses. The overarching goal of these lines of research is to better constrain the long-term effects of invasive species on biodiversity change, a topic of concern for mitigating the modern biodiversity crisis.

PaleoNICHES: Digitization of fossil collections

Our lab is currently funded through NSF Thematic Collections Network program to lead the digitization efforts for several museum collections of Cincinnatian fossils through our "Digitizing Fossils to Enable New Syntheses in Biogeography – Creating a PALEONICHES-TCN” (TCN stands for) grant. Our efforts are part of a large project in colloboration with Bruce Lieberman (Kansas) and Jon Hendricks (San Jose State) which is detailed on the Digital Atlas of Ancient Life website. The focus of our lab is to digitize the Ohio Unversity fossil collections, facilitate increased digitzation effortsfor the collection of Co-PIs Dr. Brenda Hunda (Cincinnati Museum Center) and Dr. Kendall Hauer (Miami University) and to develop an online digital atlas for identificaiton of Cincinnatian fossils: The Digital Atlas of Ordovician Life. This project is related to a broader natural history specimen digitization effort supported by the National Resource for Advancing Digitization of Biodiversity Collections (ADBC) called Integrated Digitized Biocollections, or iDigBio.

 

 

Quantitative Methods in Paleobiogeographic Analysis:
GIS Methods and Phylogenetic Biogeography

The primary area of investigation in my lab emphasizes the interplay of historical (phylogenetic and contingent) and ecological (interactions with the abiotic and biotic environment) in determining the limits of biogeographic ranges of species, and how shifts in environmental parameters manifest in shifting or splitting of geographic ranges. These shifts or splits, also known as dispersal and vicariance, form the basis for both speciation and extinction. Thus understanding the drivers of these biodiversity processes is important for understanding the role of environmental factors on evolution of life through time. Biogeographic patterns are assessed within two quantitative frameworks: GIS-based analysis and phylogenetic biogeography.

GIS-based analyses involve reconstructing the range of fossil taxa from museum and field collected occurrence data to produce polygon estimates of individual species ranges through various time slices. (PDF detailing polygon range reconstruction methods). In addition, ecological niche modeling (ENM) methods are employed in which sedimentological proxies, such as substrate type, water depth, etc., are used in a computer-learning based environment to rigorously predict the fundamental niche of species. Predicting the fundamental niche provides a null hypothesis against which to compare observed ranges of taxa and quantitatively assess which environmental parameters control observed geographic range shifts through time. Niche modeling of Devonian brachiopods (Stigall Rode and Lieberman, 2005) demonstrated the importance of timing of range expansion in survival through the Late Devonian Biodiversity Crisis. "Ground truthing" in the field has shown ENM methods to be highly accurate for modeling the ranges of brachiopods in the Late Ordovician (Walls and Stigall, 2012). GIS-methods have also been employed to analyze biogeographic patterns in Cambrian soft-bodies taxa (Hendricks et al., 2008) and Miocene horses (Maguire and Stigall, 2009). Currently, GIS efforts are related to studying the Late Ordovician faunas of the Cincinnati Arch (Stigall, 2010, 2012, 2014; see below).

Phylogenetic biogeography utilizes cladograms derived through phylogenetic systematics combined with biogeographic information on species distribution to determine the relationships (relative times of connection and isolation) of biogeographic regions. (Stigall Rode and Lieberman, 2005; Wright and Stigall, 2013), and analyses of Gondwanan vertebrate biogeography is currently in progress with Pat O'Connor and Nancy Stevens here at OHIO.

Role of Invasive Species in Mediating Biodiversity Crises

Invasive species, species which colonize a region outside their ancestral range and subsequently spread, are one of the primary causes of the current biodiversity crisis facing our planet.  Although many recent species invasions are due to human intervention, invasive species have also occurred in the geologic past.

Species invasions in the fossil record occur due to the collapse of climatic, geographic, or ecological barriers.  Dramatic spread of formerly endemic species is common during times of ecological turnover and changes from an endemic to cosmopolitan biota and can be identified by mapping ranges through time within a phylogenetic context.  Examining the causes and effects of invasive species within the fossil record better constrain the long-term (thousands of years) effects of invasive species on biodiversity. In particular, I am interested in assessing how species invasions in the fossil record effect patterns of biodiversity overturn, specifically speciation and extinction during intervals of faunal turnover.

Late Devonian Biodiversity Crisis
The first biotic crisis I am interested in is the Late Devonian (Frasnian-Famennian) Biodiversity Crisis. Although this event is sometimes referred to as a mass extinction, it is more accurately a mass loss of speciation. Work on both phylogenetic and biogeographic patterns in brachiopod, bivalve, and crustacean taxa during this interval all point to a dramatic decline in speciation by vicariance (Rode, 2004; Rode and Lieberman, 2004; Stigall Rode and Lieberman, 2005a, 2005b; Stigall Rode 2005). Episodes of dispersal, characteristic of invasive species, however, appear more common than background rates (Stigall and Lieberman, 2006; Stigall, 2010, 2012).

Late Ordovician Richmondian Invasion
The boundary between the Maysvillian and Richmondian Stage of the Late Ordovician in Eastern North America includes an episode of intense extra-basinal invasion, known as the Richmondian Invasion. Currently I am working with my students on an NSF-funded project to examine the biogeographic patterns associated with this interval using niche modeling methods in concert with phylogenetic systematics of the abundant articulate brachiopod taxa of these strata in the Cincinnati Arch region. Analyses have identify siignificant shifts in biogeographic and niche stability patterns across the invasion interval (Stigall, 2010, 2011, 2012; Dudei and Stigall, 2010; Walls and Stigall, 2011; Malizia and Stigall, 2011, Brame and Stigall, 2014).

Methods for Analysis of Speciation Mode and Rate

To determine how factors, such as species invasions and ecologically mediated range shifts, effect faunal dynamics, it is critical to consider both speciation as well as extinction. Speciation events can only be tightly constrained when analyzing taxa within a phylogenetic framework.

Phylogenetic frameworks provide a mechanism to assess:
(1) the biogeography of speciation, in particular to differentiate the styles of allopatry: vicariance vs. dispersal (top right diagram, Rode, 2004; Stigall Rode, 2005, Wright and Stigall, 2013)
(2) determine more accurate timing using sister lineages; phylogenetically constrained speciation rates can then be used to assess timing of changes in faunal dynamics as in the diagram at the lower right (Stigall, 2008)

Combining these two types of information provides evidence for reduction in Late Devonian speciation rates due to shutdown of vicariant speciation during this interval (Stigall, 2008, 2010, 2012). Preliminary analyses of the Richmondian Invasion suggest a similar effect, indicating that the primary long term effect of invasive species may in fact be speciation depression, not elevation in extinction levels (Stigall, 2010).


   
Phylogenetic Systematics of Brachiopod and Crustacean Taxa

As noted above, analyses of biogeographic change and faunal dynamics are much more robust when completed within a phylogenetic framework.The reconstruction of these phylogenetic relationships allows more accurate assessment of speciation patterns and rates, biogeographic patterns, species invasions, etc.  The reconstruction and subsequent utilization of these phylogenetic relationships are a critical component in integrating macroevolutionary processes with biogeography, paleoecology, and paleoenvironment.

Consequently, most studies in our research group involve phylogenetic analysis of representative taxa within the biota. Taxa most frequently phylogenetically analyzed include brachiopods (Stigall Rode, 2005, Wright & Stigall 2013, 2014), bivalves (Rode, 2004), and crustaceans (Rode and Babcock, 2002, Rode and Lieberman, 2003). Species level analyses of key genera within the Cincinnatian fauna are ongoing.

Taphonomy of Weakly Biomineralized Arthropods

Understanding how fossilization occurs for taxa that are non-biomineralizing or only weakly biomineralized is an area of special concern when considering the fossil record of crustaceans. I am particularly interested in the fossilization processes present in lacustrine deposits and focus this effort on spinicaudatans (see below). This taphonomic research is in conjunction with Derek Briggs (Yale), Loren Babcock (Ohio State), and Steve Leslie (James Madison Univ.).

The initial impetus for this work was based on field collections from Jurassic lacustrine deposits of the Tranantarctic Mountains that I helped assemble in the austral winter of 2003-2004. Work on these specimens has demonstrated that the same species of conchostracans, living in essentially contemporaneous and geochemically similar lakes can be preserved very differently based on the presence of microbial mats in the environment (Babcock et al., 2006). Where microbial mat structures are absent (top 2 at right), specimens are preserved in their original skeletal composition of apatite; however, where microbial mat textures are present (below right), very little original carapace material remains and specimens are silicified (Stigall et al., 2008).

Comparison of conchostracan specimens from other deposits (Cretaceous of Madagascar, Jurassic of the Newark and North Carolina Rift Basins, Pennsylvanian of Ohio) suggest this pattern may be a common features of lightly biomineralized taxa. Future experimental work is planned to assess this aspect of arthropod taphonomy.


Systematics of Spinicaudatans ("Conchostracans")  

The Order Spinicaudata (often also referred to by the paraphyletic term "Conchchostraca") is a key group of crustaceans inhabiting lacustrine environments. These organisms are useful paleoecologically as diagnostic indicators of ephemeral pond environments and are excellent organisms for ontogenetic studies since they retain rather than molt their carapace during growth stages.

While Spinicaudatans have been frequently incorporated into faunal lists of continental ecosystems, there has been relatively little work on their systematics and no analyses involving phylogenetic systematics of these organisms have been conducted. Due to the nature of ontogenetic changes in carapace ornamentation, systematic work conducted prior to scanning electron microscopy often was unable to recognize the synapomorphies of major clades, and consequently requires reanalysis.

Systematic revision of these organisms began by revising some of Paul Tasch's types as part of the Antarctic Project, but has expanded further into describing new material from the Cretaceous of Madagascar (Stigall and Hartman, 2008), Jurassic of Namibia (Stigall et al. 2014),Miocene of Montana, and preliminary investigations of Pennsylvanian species of the Midcontinent, Jurassic species of the North American Rift Basins, and Jurassic of the Morrison Formation.

Understanding ontogenetic changes in carapace ornamentation is a key part of this project and involves growth of modern spinicaudatans with the assistance of Steve Weeks (U. Akron) and in coordination with the Univ of Akron ESEM lab run by Lisa Park.

back to top

 

Copyright © 2007-2012 Alycia Stigall
Web page last updated 1/24/14
Email webmaster