Tar Pit Beetles Unlock New Clues to Ice Age Climate in Southern California

Preliminary analyses of Tar Pit insects provide evidence for more aridity and warmth than previously proposed for the transition from late Ice Age to modern times.

by Anna Holden, American Museum of Natural History, La Brea Tar Pits and Museum

Establishing Paleoclimate as a Means to Understand Current Climate Change

Scientists from the American Museum of Natural History, La Brea Tar Pits and Museum, UC BerkeleyUC, Irvine, and the California Academy of Sciences (CAS) are joining forces in an effort to use information from fossil insects to help establish what the Ice Age climate was like in southern California. This project is intended to help us answer questions such as: “To what degree can we predict the possible future climate of California from analogous, prehistoric data?”  and “How have the flora and fauna responded to climatic changes over time?”

In California, we are currently experiencing one of the worst prolonged droughts in our recorded history (National Climate Assessment). While anthropogenic climate change may be one force driving the current episode, paleoenvironmental records indicate that this drought is not unique in the history of the region.

Although climate change impacts in southern California are well documented, our records only go back a century and a half at most. Deeper paleoenvironmental patterns must be reconstructed using other evidence. The Rancho La Brea (RLB) Tar Pits in southern California offers a wealth of fossils that can shed light on how the local environment has changed through time and these reach much further back than human records.

ARH_CR_moth

Leading the project, Anna Holden, Ph.D. candidate at the Richard Gilder Graduate School, American Museum of Natural History and Research Associate, La Brea Tar Pits and Museum

Insects as Paleoclimate Indicators 

Though there is an abundance of insect material in the RLB deposit, this potential source of data has seen little use. Thanks to recent advances in reliable radiocarbon dating of disarticulated, identifiable beetle fragments from RLB (Holden and Southon, 2016), we are now in a position to date radiocarbon time as far back as 50,000 years or more, and are also able to date sufficient numbers of insect fossils such that they can provide a significant density of data for this period.

These developments have now been combined with methods using carabid and tenebrionid beetles as climate indicators. We can use these beetles as their present-day life-cycles, climate restrictions, and geographic distributions of the selected species are relatively well documented, and unlike migrating and often wide-ranging, mammals and birds, they offer crucial information about very local environments. Beetle species known from the Quaternary and even Tertiary are still extant and can reasonably be assumed to have flourished under the same climatic conditions that they do today.

d_dilatatus

Live Dicheirus dilatatus imaged by Joyce Gross, UC Berkeley

A number of species of carabids and some tenebrionids have been used as paleoclimate indicators over the past decades. In particular, these predatory and scavenging species, whose behavior is reasonably well-documented, are known to find food in a variety of habitats and are not tied to specific types of vegetation. They are able to migrate into suitably warm or cool, wetter or drier habits, independent of the flora, as necessary. Therefore, they are expected to typically respond to fluctuations faster than plants (Elias, 2010).

RLP 15216E prothorax

Prothorax of fossil  Dicheirus dilatatus imaged by Carrie Howard, La Brea Tar Pits and Museum

Give this, generalist predator and scavenging insects may serve as better local indicators of change—in contrast, there may be a lag of hundreds of years for evidence of temperature changes to appear in pollen records (Elias, 2010). We expect that the rapid changes in populations of insects such as carabids and tenebrionids can reflect climate change that takes place within a matter of decades. Already entomologists are tracking the distribution of present day carabids and tenebrionids to record how they respond to current climate change.

 



 

Advances in Radiocarbon Dating Circumvent the Lack of Biostratigraphy* at RLB

john_southon copy

Dr. John Southon, collaborator and co-founder of the UC Irvine Keck Carbon Cycle Mass Spectrometry Facility

For our initial step, we established a protocol to remove the asphalt matrix and other fossil preparation contaminants from the insect cuticle. This protocol works so effectively that it is now considered the most accurate procedure for radiocarbon dating insect cuticle from any Late Pleistocene deposit.

This method is invaluable for material from the  RLB which lacks biostratigraphy as a means of establishing dates by association.  Asphalt flows are characteristically intermittent and discontinuous and the result is mixing of fossils from different ages into the same layer.


  • *Biostratigraphy: Layers, or “strata,” in which the fossils are assumed to correspond to the same age. Strata form and superimpose over time and are one of many layers.

 

Selecting the Right Insects for Analysis

The next step was to identify disarticulated fragments of carabids and tenebrionids with well-documented, narrow climate restrictions. Species also must be abundant enough in the RLB for destructive sampling and have enough mass to survive the chemical baths and then still have sufficient material remaining for radiocarbon combustion.

small Copy of 2014_07_05_012

Rolf Aalbu, searching for tenebrionid beetles in California.

Kip Will (UC, Berkeley) and Rolf Aalbu (CAS associate) identified and contributed critical information on the ecology of the selected carabid and tenebrionid species. Systematists such as Kip and Rolf are fundamental to the success of this project because of their expertise in California species. They spend an inordinate amount of time in the field—thus, their experience on the ground, observing the behavior and the environments where their focal taxa live, provides the necessary, first-hand, detailed habitat information.

Extracting Climate data

We then associated a suite of informative bioclimatic variables from weather station data at Worldclim.org with hundreds of georeferenced natural history records for each species from CalBug, an open-access repository of occurrence data for California arthropods with contributions from thousands of collectors and data entry personnel. Selecting suitable records from those available for each of the target species resulted in a high-resolution data set.

Preliminary Results

So far, we have radiocarbon dated approximately 200 carabids and will soon have dates for 55 tenebrionids. The insect-based results are similar to what was found by Heusser et al. (2015) but notably different in one regard- there is no evidence for an earlier mesic interval. What might explain the difference?

climate graph-arid-mesic copy

A: A concatenation diagram of radiocarbon dates based on insect data. All the sample so far have dates between the Late Pleistocene and Holocene, except for the Last Glacial Maximum (LGM) period, which is unrepresented. This is interpreted as a case of consistent aridity and warmth except during the LGM period. Absence during the LGM is likely due to climate cooling. B: A concatenation diagram of radiocarbon dates based on pollen data from  the sites nearest to RLB, including terrestrial pollen cores from lake Elsinore in Riverside County analyzed by Heusser et. al (2015), which is closer than the frequently cited Santa Barbara marine cores (Heusser et al., 1998).

Can distant pollen data adequately capture conditions at or near RLB and nearby locales? If we look at current conditions, it suggests that this may not be the case. Lake Elsinore is approximately 70 miles away, significantly farther from the ocean, and sits at nearly 400 meters above sea level compared to only about 50 meters above sea level at RLB. Therefore, assuming the two sites were equally dissimilar in the past, these paleoclimatic differences can easily be accounted for by microclimate differences between Elsinore and RLB.

 

GE_RLB_LE

Map showing terrestrial pollen core site near Lake Elsinore and the location of the Rancho la Brea

How are these results novel?

These results challenge the widely-accepted interpretation of the paleoenvironment at RLB during the Late Pleistocene as being a cool, mesic climate, similar to that of modern-day Monterey, California (which is 450km north of RLB), or having approximately twice the amount of rainfall as typically falls at RLB now.

The standard story is largely based on a remarkably small number of plant identifications that have problematically been associated with 26-29,000 year old bone collagen dates (Friscia et al., 2008; Coltrain et al., 2004) from one RLB deposit, “Pit 91.”

Surprisingly, the dated insects from Pit 91 show a broad range from late Pleistocene to Holocene in the same grids where they are associated with the much narrower bone collagen-based date range; a clear demonstration of the RBL’s lack of biostratigraphy. This emphasizes the need to date individual samples and be very cautious about relying on dates based solely on associated samples. Reliance on such associations has led to persistent, and apparently mistaken paleoenvironmental and taphonomic inferences.

Why do our samples of insects show such a wide spread of ages? Intermittent and shallow asphalt pooling, not deep enough to immobilize larger animals, may have entrapped smaller organisms such as insects just like a pitfall trap that was opened sporadically to sample active and abundant species.

Previous investigators have provided some evidence for the paleoenvironment of southern California during the late Quaternary, but we still lack important details. Using the insects of RLB as climate and taphonomic indicators we can more clearly evaluate RLB’s significance for understanding other events such as the timing and agency of the megafaunal extinctions.

Stay tuned for even more results and other studies which use RLB insect fossils to better understand changes in southern California flora and fauna over time.

Acknowledgements

Many thanks to the scientists, staff and volunteers who have collected and input CalBug data required for this study. We also thank the scientists and staff at the La Brea Tar Pits and Museum and the American Museum of Natural History.

References

Coltrain, J., Harris, J.M., Cerling, T.E.,  Ehleringer, J.R., Dearing, M., Ward, J. and J. Allen. 2004. Rancho La Brea stable isotope biogeochemistry and its implications for the palaeoecology of late Pleistocene, coastal southern California. Palaeogeography, Palaeoclimatology, Palaeoecology 205(3–4):199-219.
Elias S. 2010. Advances in Quaternary Entomology, Amsterdam: Elsevier, 3017 p.
Friscia A.R., Van Valkenburgh B., Spencer L., Harris J.M. 2008. Chronology and spatial distribution of large mammal bones in Pit 91, Rancho La Brea. Palaios 23:35-42.
Heusser, L.E., Kirby, M.E., Nichols, J.E. 2015. Pollen-based evidence of extreme drought during the last Glacial (32.6–9.0 ka) in coastal southern California. Quaternary Science Reviews 126:242-253.
Heusser, L.E. 1998. Direct correlation of millennial‐scale changes in western North American vegetation and climate with changes in the California Current system over the past∼ 60 kyr. Paleoceanography 13.3: 252-262.
Holden, A. R., and J. R. Southon. 2016. Radiocarbon Dating and Stable Isotopic Analysis of Insect Chitin from the Rancho La Brea Tar Pits, Southern California. Radiocarbon 58(1): 99-113.

 

 

Posted in Uncategorized | 2 Comments

Ramp traps: A simple design

Together with a group of undergraduate students, I am comparing the trapping efficiency of standard pitfall cups and ramp traps. Preliminary results suggest that the ramp traps perform quite well. They catch a similar diversity of insects and don’t trap as many non-target critters like lizards and salamanders. But, we are still sorting and identifying samples from the Hopland Bioblitz, where we ran the traps, so I don’t have the final word yet.

 

DSCN0502

Trap components- Left to right, sheet metal flashing square; a pair of ramps; modified pipette tip box trap

 

The basic trap components are shown in the image above. The ramps are made from 5x7in sheet-metal flashing (on left) that you can buy at a hardware store in packs of 10. It would be cheaper to cut your own, but then you have to cut a lot of sheet metal, which is a hassle. For me, the precut pieces are worth it. Each ramp (in middle) has the sides bent up about 3/8in and a small tab cut and bent (image below) so that it fits and is held in the notch in the box. The box (on right) is a standard, empty pipette tip box with a notch cut out of each side. The lid is a handy, snap-on rain shield.

 

The sheet metal is slippery and so to make it rough and easy for insects to climb up, the inner surface of the ramp is painted with a mixture of metal priming paint and clean playground sand.

Assembled, the trap looks like the images above. When set up the field propylene glycol is put in the box. When you place the trap, be sure to push the ends of the ramps down into the dirt or leaf litter so that insects will walk right up the ramp and not go under it.

Building the traps takes more work than just going to the store and buying cups, but in the field, there is no digging, which means they can be set up quickly and easily. In the paper based on our study, we will explore in detail the pros and cons of each trap style, but it seems clear that ramp traps have a place in our standard insect collecting kit.

Posted in Uncategorized | 1 Comment

Ramp v. Pitfall

Part of the Hopland Bioblitz effort is comparing two styles of traps for ground active arthropods, ramp traps and pitfall traps. There is a lot more sorting and identifying to do, but the tenebrionid catch visually appears to tell us something. Just in terms of absolute numbers of tenebrionid beetles, the ramp (R) traps did about the same as the pitfalls (PF) for habitats 1-4. Habitat 5 looks different.

Tenebs1

Samples from Hopland REC. Ramp traps (R) and Pitfall traps (PF) from sites 1-4.

 

Posted in Uncategorized | 1 Comment

Hopland REC’s blind silverfish brought to light at the bioblitz

 

8s4a7667

An immature, blind soil-dwelling silverfish (Zygentoma: Nicoletiidae) found at Hopland REC. (about 6mm long) Photo by Joyce Gross.

 

The recent Hopland Bioblitz was a chance to really dig in and sample insects. One exciting find was a wee beastie in a family of silverfish that is very little-known in California. These blind soil-dwellers were only recently recognized from the state when a new species was described from Mt. Diablo just two years ago [1]! Three specimens were found during the bioblitz effort appear to be another undescribed species (see image above). Two individuals were first collected in buried traps and the third was found by searching under rocks at night in a cool gully on the property.

We continue to sort and identify the insects and spiders collected during the bioblitz and expect to report  more new records and new species.

Espinasa, L. and Botelho, J.  (2014) A New Species of Speleonycta (Insecta: Zygentoma) from the Bay Area of San Francisco, California. Proceedings of the Biological Society of Washington. 127(2): 335-339.

p.s. I want to mention I collected two nicoletiids at Mangini Ranch near Mt. Diablo in 2013 in buried traps but didn’t know their significance at the time.

Posted in Uncategorized | Leave a comment

Participate in our bioblitz online

Please share: You can participate remotely!

Our big Hopland scientific bioblitz is this weekend (9-10 April, with some events on the 8th) and I look forward to seeing some of you there. If you can’t make it to HREC, there are many ways you can remotely help us and check out what is happening all weekend long.

HELP US OUT. http://www.inaturalist.org/ Many people will be using iNaturalist to make and share observations. Helping out the effort is easy. Look for observations at the iNaturalist site by searching for “Hopland” in the “Projects” pulldown menu and choose “Hopland Research Extension Center”. Once there, you can browse the plants and animals needing identification and needing confirmation. Every identification counts toward our goal of massively increasing the knowledge of the HREC’s flora and fauna.

VOTE ON IMAGES. http://www.hoplandbioblitz.org/ We are hosting an image contest for the plants and animals of HREC. Great prizes will be given for images that get the most votes(REI gift cards and a GoPro grand prize!). Please visit the site and vote for your favorites frequently during the weekend and share them and then sit back and what the slide show.

CHECK US OUT. http://geoportal.ucanr.edu/# Our new app will graphically show you our progress for the bioblitz observations. Results will be updated every 15 minutes. See how your favorite groups are doing in the challenge to document as many species as possible.

Look for #HoplandBioblitz on Twitter and Instagram

Follow along on Facebook https://www.facebook.com/HoplandREC/

 

Posted in Uncategorized | 2 Comments

Two Ph.D. student positions available at UCB and SDSU

Students will be team members in an NSF-funded multidisciplinary research project: The Genetic Basis, Biosynthetic Pathways and Evolution of Geadephagan Chemical Defense that includes collaborations among researchers at UC, Berkeley; San Diego State University; University of Arizona; and Steven’s Institute of Technology.

The Will Lab, ESPM Department and Essig Museum of Entomology, University of California, Berkeley, is seeking a graduate student interested in working on understanding the function and evolution of defensive chemistry in Adephagan beetles with a preference for students with a master’s degree and a background or strong interest in insect chemical ecology, molecular biology and phylogenetics. This student could start as soon as fall 2016 if he/she makes the 1 Dec 2015 application deadline (http://ourenvironment.berkeley.edu/graduate-programs/admissions/), but if not filled in 2016, this and additional positions may be open in 2017.

The Renner Lab, Evolutionary Biology, San Diego State University, is searching for a graduate student with a background or strong interest in molecular evolution, phylogenetics, and bioinformatics. This student could start as early as fall 2016 if he/she makes the December 14th priority deadline (http://www.bio.sdsu.edu/eb/jdapplications.html), but if not filled in 2016, this position may be open in 2017.

Short project  summary (see also this post)

Geadephaga is the largest clade of organisms that use a single homologous gland system to produce no less than 19 distinct classes of chemical compounds for defense. This project will develop a detailed functional and evolutionary understanding of defensive chemistry evolution by focusing on eight species from the four lineages of quinone producing carabid beetles, including four species commonly known as the bombardier beetles, which chemically blast their defensive quinones at extremely hot temperatures (up to 100 °C). Using a multidisciplinary approach, this project will identify and comparatively examine transcriptomes for genes involved in quinone production, elucidate chemical biosynthetic pathways, and describe the genetic architecture of quinone evolution. From gland-specific transcripts candidate genes related to the production of defensive secretions will be identified and gene function will be validated experimentally by blocking gene transcription and looking phenotypic changes in compounds produced and transcription activity in the chemical secretory cells. Biosynthetic pathways of quinones will be confirmed by injection of labeled amino acid precursors and analysis of compounds produced in the beetles’ glands. In order to study the evolutionary history of quinone biosynthesis in carabids we will infer the phylogenetic history of candidate gene families and the tree topology and branch lengths will be analyzed to test whether genes are ancient and shared among taxa, or if gene diversification is recent and specific to certain lineages. We will test the hypothesis that the genes up-regulated in secretory cells during quinone synthesis are closely related to those involved in quinone production in arthropod cuticle. Thus the project will empirically address the well-known, but untested, scenario of how the bombardier beetle evolved its explosive defense abilities. With the bombardier beetle as a model, the project will help develop elementary school level lesson plans on topics in chemical ecology and biological chemical defense evolution that will reinforce the Next Generation Science Standards. Additional outreach materials will be produced including a high-quality children’s book and web-based resources will be produced that target the prevalent misinformation about bombardier beetle evolution found online.

Posted in Carabids, Entomology | Leave a comment

DIY, heavy-duty, weather-proof UV light and photo-switch system

Perhaps you are like me and need to run a UV light for insects even when it rains, or especially when it rains (think rain beetles). I have chewed through a bunch of the off the shelf UV lights over the years because they are not made to get wet. Neither the ballast nor the photoelectric switch from BioQuip is designed to be exposed to rain. Plastic bags and duct tape can only do so much.

At lest BioQuip is up front about the limits of their gear.

At lest BioQuip is up front about the limits of their gear. “Protect from dampness?” When am I not damp in the field?

Given my need for a ‘rain or shine light,’ I looked at the kind of materials used in off-road vehicles, marine applications and home, 12 volt solar systems to see what was being used to run lights that must stand up to the elements day in and day out.

The system I built has a number of advantages over the pre-made systems; 1. minimum 16 gauge wire for better flow of current and less heat, 2. fully sealed aluminum circuit box protects the ballast from water and acts as a heat sink, 3. in-line fuse protects ballast from over amping, 4. the marine-grade photoelectric switch is completely weather proof.

The cost of materials is very similar to the pre-made systems, with the DIY one a bit cheaper ($115 v. $134).

Itemized list of items needed to make the UV light system w/switch and costs compared to standard BioQuip equivalent. Shipping and tax not included in prices.

Itemized list of what is needed to make the UV light system w/switch and the costs compared to the standard BioQuip equivalent. Shipping and tax not included in prices.

The BioQuip light + switch system is smaller and lighter. If you need light weight for a long hike then this is not the design for that. If you use cheaper materials you can make a very basic fair weather light cheaper still, but you get what you pay for. There is the advantage that when you buy a system you don’t spend the time and effort to build it and if it fails you might be able to return it for repair or replacement (But not if you leave it out in the rain. Remember “protect from dampness.”)

But if you like to DIY then here is some more information that can help you see how I built mine.

The complete system looks like this. The numbers refer to items in the table above. The wires are quite short for my application, but given the gauge they could be much long and still work very well.

The complete system looks like this. The numbers refer to items in the table above. The wires are quite short for my application, but given the gauge they could be much long and still work very well.

This shows the circuit box with the ballast mounted inside. The red 'a' indicates where I drilled a hole to run the wires through the external mounting holes. This was then filled with marine-grade silicon sealant (10).

This shows the circuit box with the ballast mounted inside. The red ‘a’ indicates where I drilled a hole to run the wires through the external mounting holes. This was then filled with marine-grade silicon sealant (10).

In order to hold the ballast firmly in the circuit box I made a small clip out of sheet aluminum (c) and used the tab on the ballast (a) to hold one end and the internal grounding screw (b) to mount it to the box.

In order to hold the ballast firmly in the circuit box I made a small clip out of sheet aluminum (c) and used the tab on the ballast (a) to hold one end and the internal grounding screw (b) to mount it to the box.

The photoswitch (4) was mounted using one of the box's external mounting hole and the wires were run out the other. Marine-grade silicon sealant (10) was used to seal around the wire exit hole.

The photoswitch (4) was mounted using one of the box’s external mounting holes and the wires were run out the other. Marine-grade silicon sealant (10) was used to seal around the wire exit hole.

The end of the tubes fit perfectly into a cut off standard 50ml centrifuge tube that was drilled for the wires (b). The ends then are wrapped in shot sections of the tube mesh cover and secured with a zip-tie (11).

The end of the tubes fit perfectly into a cut off standard 50ml centrifuge tube that was drilled for the wires (b). The ends then are wrapped in short sections of the tube mesh cover and secured with a zip-tie (11).

Posted in Entomology | Leave a comment